1. Where is the book?

2. What did they look after a long walk?

3. What make people different from all other animals?

4. Who is Jane waiting for?

5. Why did you have to cancel your picnic?

6. How long does it take to ride to VT by motorbike?

7. Who is Mimi talking to Fred about?

8. How often do you go to E club?

9. Why do you often go for a walk at night?

10. Where are you going for holiday this summer?

11. Who is your father going to take to the zoo next Sunday?

12. What do you study English for?

help me all

4 If you aren't alert, you computer will be infected with viruses

5 If we use much pesticide on vegetables, they will become poisonous

9 Because Nam needs to improve his social skills, he attends the activity

11 How about using public buses instead of motorbike 

12 They enjoy protecting the environment unpolluted 

15 Mr Brown was disappointed that his son didn't write to him

8d

9c

10d

11a

12d

Câu 12: C

Câu 12 : A

D

12. have been

10. built

11. was talking

12. have been

13. were eating

8 disappointing

12 preservation

13 seriously

Ta có:

\(v_{tb}=\dfrac{S_1+S_2}{t_1+t_2}=\dfrac{S}{\dfrac{S_1}{v_1}+\dfrac{S_2}{v_2}}=\dfrac{S}{\dfrac{\dfrac{1}{2}S}{v_1}+\dfrac{\dfrac{1}{2}S}{v_2}}=\dfrac{S}{\dfrac{S}{2\cdot12}+\dfrac{S}{2\cdot20}}=15\)km/h

Chọn A

D