17. We/ought/ submit/assignment/ tomorrow. a. We ought submit our assignment tomorrow. b. We ought to submit our assignment tomorrow. c. We ought to have submitted our assignment tomorrow. d. We ought have submitted our assignment tomorrow. 18. We/ hardly/ understand/ him/ because/ his accent. a. We hardly ever can understand him because of his accent. b. We may hardly understand him because his accent. c. We hardly understand him because he has his accent. d. We can hardly understand him because of his accent. 19. he/ retire/ eldest son/ take over/ business. a. After he retired, his eldest son took over his business. b. After retiring, his eldest son will take over his business. c. After he retires, his eldest son will take over a business. d. After he has retired, his eldest son took over a business. 20. The patient/ recover/ more/ rapidly/ expected. a. The patient recovered rapidly he expected more than. b. The patient has recovered more rapidly he expected. c. The patient recovered more rapidly than expected. d. The patient rapidly recovered than he more expected.