18. If we go on littering, the environment...

• B. will become is the correct answer. This is a conditional sentence, and the future tense is used to express a likely outcome.

19. The boy was very hungry...

• A. so is the correct answer. It indicates a cause-and-effect relationship between the boy's hunger and his action of eating.

20. The man suggests...

• C. going is the correct answer. The verb "suggest" is followed by the gerund form of the verb.

21. A dripping faucet...

• A. can waste is the correct answer. It expresses a possibility or potential.

22. He sighed...

• A. sadly is the correct answer. It describes the manner in which he sighed.

23. Please... the lights. It's very dark.

• A. turn on is the correct answer. It is the appropriate phrase to request switching on the lights.

24. Not only... her father, but you...

• B. will you meet is the correct answer. The parallel structure requires the same verb tense for both clauses.

25. The man sat down on the chair...

• B. and is the correct answer. It connects two independent clauses.

26. You should travel by bike...

• B. instead of is the correct answer. It expresses an alternative to traveling by motorbike.

27. Please go... with what you're doing. Don't look at them!

• B. on is the correct answer. It means to continue with an activity.

28. The new appliance...

• C. effectively is the correct answer. It is an adverb modifying the verb "works."

29. Anne: "I think that's worth celebrating. Don't you agree, Charlie?" Charlie:

• A. Yes, I do actually. is the most polite and affirmative response.

30. Tom: "You've got a lovely singing voice, Mary." Mary:

• D. Yes, I think so. is a polite and modest response to a compliment.

• If we go littering, the environment B. will become seriously polluted.

• The boy was very hungry D. but he ate nothing.

• The man suggests B. going to the seaside in the summer.

• A dripping faucet A. can waste 500 liters of water a month.

• He sighed A. sadly when he heard the news.

• Please A. turn on the lights. It's very dark.

• The man sat down on the chair B. when he began to tell the story.

• You should travel by bike B. instead of motorbike to save energy.

• Please go A. on with what you're doing. Don't look at them!

• The new appliance does not only work B. effectively but also saves energy.

• Anne: "I think it's worth celebrating. Don't you agree, Charlie?"
  Charlie: "D. Yes, I think so."

• Tom: "You've got a lovely singing voice, Mary."
  Mary: "A. No, I actually..." (Note: this response might seem incomplete; a more typical response could be "Thank you!" but given the options, this one fits the context.)

đáp án:

1. A. becomes
2. D. but
3. B. going
4. A. can waste
5. A. sadly
6. A. turn on
7. B. when
8. B. instead of
9. A. on
10. B. effectively
11. D. Yes, I think so.
12. A. No, I actually...