17. The cost is expensive. -> It is expensive.
18. I have a promise with him at 6 -> I make a promise with him at 6.
19. Most of people are afraid of death. -> Most of people are afraid for death.
20. The department store is attracting a lot of clients by lowering prices. -> The department store is attracting a lot of clients with low prices.
21. He speaks English very good. -> He speaks English very well.
22. She's not saying the truth. -> She does not say the truth.
23. The company is very incompetent in the fast-food market. -> The company is very incompetent for the fast-food market.
24. He became mad when he heard the news. -> He was mad when he heard the news.
25. She drives very fastly.-> She drives very fast.
26. I don't know he is honest. -> I don't know that he is honest.
27. He didn't mind to show me the way to the hotel. -> He didn't have a mind to show me the way to the hotel.
28. Did you go to swim yesterday? -> Did you go swimming yesterday?
29. He's busy to read books. He is too busy to read books.
30. They are doing their best to search missing people in the accident. -> They do their best to search missing people in the accident.
16. correct. 17. The cost is high. 18. I've promised to meet him at 6 p.m. 19. Most people are afraid of death. 20. The department store is attracting a lot of clients customers by lowering prices. 21. He speaks english very well. 22. correct 23. correct 24. Choose either "became angry" (more formal) or "got mad" (informal). 25. She drives very fast. 26. I don't know if he's honest. 27. He didn't mind showing me the way to the hotel. 28. Did you swim yesterday? 29. He's busy reading books. 30. They're doing their best to seach for the missing people in the accident.