从下列各题所给的四个选项中选择正确的一项。 　　　 　　12. Jacks father is ______ doctor. 　　A. a B. an C. some D. / ( ) 　　　 　　13. He often does some washing ________ Sunday. 　　A. at B. in C. on D. by ( ) 　　　 　　14. This room is ours,and that one is _______. 　　A. they B. them C. their D. theirs ( ) 　　　 　　15. Tom is ________ boy in his class. 　　A. tall B. taller C. tallest D. the tallest ( ) 　　　 　　16. Can you come here next Friday? Sorry,I ______. 　　A. cant B. mustnt C. neednt D. may not ( ) 　　　 　　17. Did you _______ the football match last night? 　　A. see B. watch C. look D. read ( ) 　　　 　　18. There _______ many high buildings in this city. 　　A. is B. are C. have D. has ( ) 　　　 　　19. John has two brothers. One is an artist, _______ is a scientist. 　　A. the others B. another C. the other D. others ( ) 　　　 　　20. The man asked the policeman ________. 　　A. let him to go B. to let him to go 　　C. let him go D. to let him go ( )