4. have learned, was

5. Have you ever been, haven't been, will be

6. have done, got

7. joined, was, has served, went

8. have we lived, have lived

9. finished, has been

10. have gone

I. 

1. hotter

2. drier

3. smaller

4. older

5. wider

6. more delecious

7. cheaper.

II.

1. Viet Nam is colder than Sweden.

2. The Andes is the longest mountain ranges in the world.

3. A car is often more expensive than a bike.

4. HCMC is noisier than Hoi An.

4. The air in the city is often not as clean as that in the countryside.

5. Câu này đề phải là Ba Be Lake í bigger than all the other natural lakes in Viet nam.

-> Ba Be Lake í the biggest lake in Viet Nam.

III.

1. hottest

2. longest

3. highest

4. largest 

5. best

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$\text{~ Nếu được thì cho mk trả lời hay nhất nha! ~}$