When and why he came here ________ yet. A. is not known B. are not known C. has not known D. have not bee 12. I wonder how much ________. A. does the watch cost B. did the watch cost C. the watch costed D. the watch costs 13. Mary is ________ someone might recognize her. A. afraid of B. afraid about C. afraid that D. afraid for 14.________ is no reason for dismissing her. A. Because she was a few minutes late B. Owing to a few minutes late C. The fact that she was a few minutes late D. Why she is a few minutes late 15. They came to the conclusion _______by a computer. A. that not all things can be done B. because of not all things be done C. being not all things can be done D. because not all things can be done 16. Why the explosion occurred was ________ the laboratory attendant had been careless. A. for B. because C. since D. that 17. I don't doubt ________ he'll come. A. that B. if C. what D. whether 18. —“Why did you go to the wrong class, Mr. Wang” —“Well, I forget _______ I was supposed to go to.” A. which the room B. which room C. what was the room D. what room was it 19. Output is now six times ________ it was before liberation. A. that B. which C. what D. of which 20. Mary: Helen is a mere washer woman, yet she's now buying a big house. Carol: Yes. Because she's always saved ________. A. what little she earns B. how little she earns C. for little she earns D. with little she earns