Question: #1: Answer A is present perfect. Answer is past perfect. Both answers are grammatically correct. #7 Answer A implies an obligation. Answer C means "ought to" -- a lesser degree of obligation. #8, #16: Answer C also, simple past. #17: All answers would be grammatically correct. Answer A, implies current intent. Answer B implies a possibility. Answer C is present continuous tense. #18: "trip TO Europe." #11: Answer B also, simple past.