Task 1:

1. litter

2. contaminated

3. makes

4. environmental

5. floating

6. from

7. fewer

8. pay

9. noisy

10. to

11. have

12. dramatic 

13. action

14. population

15. about

Task 2:

1-E

2-C

3-A

4-D

5-B

Task 3:

1. People will have a clean water if we use it carefully.

I. Choose the suitable words/phrases to fill in the blanks.

1. litter (rác)

2. contaminated (ô nhiễm)

3. makes (to make it adj for sb to do sth)

4. environmental (thuộc về môi trường)

5. floating (nổi)

6. from (to prevent sb from doing sth: ngăn ai làm gì) 

7. fewer

8. pay

9. noisy (ồn ào)

10. to

11. have

12. dramatic (nghiêm trọng)

13. action

14. population 

15. about

II. Match two parts to make sentences.

1. E (If there are many trees, the air will be cleaner.)

2. C (If wild animals disappeared, our life would be threatened.)

3. A (If the air is polluted, more people will have breathing problems.)

4. D (If oil from ships were spilled in oceans and rivers, a lot of underwater animals could be died.)

5. B (If you hear music too loud, you will have some hearing problems.)

III. Use the words to make sentences.

1. People will have more clean water if we use it carefully. (Con người sẽ có nhiều nước sạch nếu ta sử dụng chúng cẩn thận.)