Hòa tan 2,3g Na vào 197,8g nước được dung dịch A và khí B.

a/ Tính C% của dung dịch A.

b/ Tính nồng độ M của dung dịch A.

Đĩa xích của xe đạp có 75 răng, đĩa líp có 25 răng. Tính tỉ số truyền i và cho biết khi đĩa xích quay 3 vòng thì líp quay mấy vòng ?

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Topic: The benefits of computers

Give the correect tense of the verbs in the brackets:

1. When we (meet)..................George and Linda yesterday, we (walk).................through the park.

2. What.......you (do)...................at eight o'clock last night? We (watch).....................TV.

3. The light (go).............out while we (have)....................dinner.

4. My mother (wait) was walking................................for me when I (come)..................home.

5. The postman (bring)........................................the letters twice a day.

6. Alice and Susan (know)...........................each other for six months.

7. Tom (not want)...............................to go to the cinema last night.

8. I (spend) will spend..............................my next summer vacation in Dalat.

9. While I was writing a letter, the children (play) were playing..............................outdise.

10. Columbus (discover).....................................America more than 400 years ago.

11. Look! The bus (come)................................................

12. Mai (brush)...........................her teeth after meals.

13. Mai and Lan (play).................................games after school.

14. Our teacher (look)................................. at our books every day.

15. She is cooking and we (do)................................the housework.

16. The younger students (not watch)...................................TV at night.

17. They (be)................................in the kitchen now.

18. Vy (listen)................................to music every night.

19. We (play)...................................soccer at the moment.

20. Where (be)................................your father now? - He (read).............................a newspaper.

Fill in the blank with one suitable preposition:

1. Are you intereested......protecting the environment.

2. There shoes are made.......old car tires.

3. I will pick you........ at the hotel.......7 o'clock.

4. They went swimming...........Waikiki Beach as soon as they arrived..........the Hawaiian issland........Oahu.

5. The ambulance will be there........about ten minutes.

6. My mother is very keen.........gerowing roses. My sister is extremely fond....... music.

7. How many members participated.........the rice-cooking contest.

8. Saints Claus is based.........the description of Saint Nicholas.