in sentence 2 there are 2 mistakes: incorrect word order and sequence of tense rule not followed.

Incorrect: First, he explained what are transistors.

Correct:  First, he explained what transistors were.

In sentence 3 there are 2 mistakes: incorrect punctuation and sequence of tense rule not followed

Incorrect: He said, that they are very small electronic devices used in telephone, automobiles, radios, and so on.

Correct:  He said that they were very small electronic devices used in telephone, automobiles, radios, and so on.

In sentence 4 there is one mistake: sequence of tense rule not followed.

Incorrect: He further explained that transistors control the flow of electric current in electronic equipment.

Correct:  He further explained that transistors controlled the flow of electric current in electronic equipment.

In sentence 5 there is one mistake: sequence of tense rule not followed.

Incorrect: He wanted to know which popular technological invention cannot operate without transistors.

Correct:  He wanted to know which popular technological invention could not operate without transistors.

In sentence 6 there are 3 mistakes: incorrect punctuation, sequence of tense rule not followed, and omitted subordinator that.

Incorrect: Most students agreed, it is the personal computer.

Correct:  Most students agreed that it was the personal computer.

In sentence 7 there are 3 mistakes: 2 times sequence of tense rule not followed and incorrect word order.

Incorrect: Professor Sanchez then asked if the students know how do transistors function in computers.

Correct:  Professor Sanchez then asked if the students knew how transistors functioned in computers.

In sentence 8 there is one mistake: sequence of tense rule not followed.

Incorrect: He said that the transistors were etched into tiny silicon microchips and that these transistors increase computers' speed and data storage capacity.

Correct:  He said that the transistors  were etched into tiny silicon microchips and that these transistors increased computers' speed and data storage capacity.

In sentence 9 there are 2 mistakes: incorrect word order and incorrect punctuation.

Incorrect: Then he asked the class when had transistors been invented?

Correct:  Then he asked the class when transistors had been invented.

In sentence 11 there is one mistake: sequence of tense rule not followed.

Incorrect: The professor said that he is correct.

Correct:  The professor said that he was correct.

In sentence 12 there are 2 mistakes: incorrect word order and incorrect punctuation.

Incorrect: Professor Sanchez then asked what was the importance of this invention?

Correct:  Professor Sanchez then asked what the importance of this invention was.

In sentence 13 there is one mistake: sequence of tense rule not followed.

Incorrect: Many students answered that it is the beginning of the information age.

Correct:  Many students answered that it was the beginning of the information age.

In sentence 15 there is one mistake: subjunctive verb not used.

Incorrect: He requested that each student chooses a topic by next Monday.

Correct:  He requested that each student choose a topic by next Monday.

In sentence 16 there is one mistake: subjunctive verb not used.

Incorrect: He suggested that the papers are typed.

Correct:  He suggested that the papers be typed.

1)The man is a professor. He's going to give a lecture to our students. 

=>The man who is going to give a lecture to our students is a professor.

Bài 1: Find the mistake then correct it

1. They asked him not give->to give that new information to anyone else

2. It took me so many->much time to learn this lesson

3. Do you know what was she doing->she was doing at this time yesterday?

4. The doctor advided->advised hẻ to go for a diet to lose weight

5. He said that he would visit me tomrrow->the next day

6. They were complete->completely right when they said that

7. The Browns decide going->to go to school tomorrow

8. Peter has two brothers, the older->elder is a policeman the younger is an engineer

1. I don't like being looked at

2. He is expected to win the election

3. They decided all the money will be given to the poor

4. I was let to use his computer yesterday

5. He is said to be the best student in his school

Professor Sanchez gave a lecture on transitors last Tuesday. First, he explained what are transistors=>transistors were. He said, that they are => were very small electronic devices used in telephones, automobiles radios and so on. He further explained that transitors control => controlled the flow of electric current in electronic equipment. He wanted to know which popular technological invention cannot => could not operate without transistors. Most students agreed, it is => was the personal computer. Professor Sanchez then asked if the students know => knew how do transitors function=> transistor functioned in computers. He said that the transitors were etched into tiny silicon microchips and that these transistors increase => increased computer’s speed and data storage capacity. Then he asked the class when had transitors been => transistors had been invented. Sergei guessed that they were => had been invented in 1947. The professor said that he is =>was correct. Professor Sanchez then asked what was the importance of this invention =>the importance of this invention was. Many students answered that it is =>was the beginning of the information age. At the end of the lecture, the professor assigned a paper on transistors. He requested that each student chooses => choose a topic by next Monday. He suggested that the papers are => be typed.

Professor Sanchez gave a lecture on transistors last Tuesday. First, he explained what transistors are. He said that they are very small electronic devices used in telephones, automobiles, radios, and other electronic equipment. He further explained that transistors control the flow of electric current in these devices. He then questioned the students on which popular technological invention cannot operate without transistors. Most students agreed that it is the personal computer. Professor Sanchez then asked if the students knew how transistors function in computers. He explained that transistors are etched into tiny silicon microchips, and these transistors increase the computer's speed and storage capacity. He also asked the class when transistors were invented. Sergei guessed that they were invented in 1947, which the professor confirmed as correct. Professor Sanchez then asked about the significance of this invention. Many students answered that it marked the beginning of the information age. At the end of the lecture, the professor assigned a paper on transistors and requested that each student choose a topic by next Monday. He suggested that the papers should be typed.

Using relative clause1. The woman spoke to me. She was very helpful -> The woman who was very helpful, spoke to me

2. The man is professor. He's going to give a lecture to our students -> The man is going to give a lecture to our students, is professor

3. The artists performed many wonderful shows. We met them yesterday -> The artists whom we met yesterday, performed many wonderful shows

5. She found a dog. Its leg was broken-> She found a dog whose leg was broken

6. They are the children. Their team won the match -> They are the children whose team won the match

7. My brother is very kind to everyone. You met his wife last week . -> My brother whom you met his wife last week, is very kind to everyone

8. Those books belong to Ann. They are on the table -> Those books which are on the table, belong to ann

9. Tom is very careless. He lost his watch yesterday-> Tom 

who lost his watch yesterday, is very careless

10. I don't like the stories. They have unhappy endings => I don't like  the stories which have unhappy endings

-Give the correct form or tense of the very in brackets:

A. After a dinner ( give )given by the Prime Minister of a little South American Republic, a ( distinguish )distinguished diplomat complained to his host that the Minister of Justice, who ( sit)had been sitting on his left. ( steal)had stolen his watch.

" Ah, he ( not do )shouldn't have done that ", said the Prime Minister. " I ( get)will get it back for you ". Sure enough, toward the end of the evening the watch ( return)was returned to its owner.

" What did he say( say ) ?" asked the diplomat

" Hush! " said the host, ( glance)glancing anxiously at him. " He doesn't know that I ( get ) have got it back ".

1. Learning English is no difficult for me.

→ It is not difficult for me to learn E

2. Jim was very confident when he said that he was the best.

→ Jim was confident to say that he was the best.

3. Peter received a letter from his foreign friend yesterday. He was very happy about it.

→ Peter was happy to receive a letter from his foreign friend yesterday

4. I can’t come to your party this weekend. I’m afraid.

→ I am afraid of not being able to come to your party this weekend

5. Doing gardening is not as easy as it looks. 

→ It is not as easy to do gardening as it looks

6. I had no difficulty in making the last decision.

→ It was not difficult for me to make  the last decision.

7. I think Peter is very happy. He has won a lottery.

→ I think Peter is happy that he has won a lottery.

8. You were so lucky. You ran into a famous singer

→ You were so lucky that you ran into a famous singer