15. It was a week before Tet and the supermarket was crowded _______ shoppers.
a. with                   b. of                            c. on                           d. for
16.   Before Jennifer won the lottery, she..............any kind of contest.
     a. hasn't entered        b. doesn't enter        c. wasn't entering        d. hadn't entered
17.   By the time he arrived at the party, all his classmates......................
     a. has left                  b. left                       c. was leaving              d. had left
18.   When I was a child, .......................the violin.
     a. I was playing         b. I had played         c. I play                       d. I played
19.   It's two years...............Joe.
     a. that I don't see                                                                         b. that I haven't seen
     c. since I didn't see                                                                  d. since I saw
20. We .......................... in New York for ten years by the time we ...........here in 1987.
     a. have lived/ moved                                                               b. lived / moved
     c. lived/ had moved                                                                  d. had lived / moved
21. Karen didn't want to come to the cinema with us because she ............. the film.
     a. has already seen                              b. already had seen
      c. had already seen                               d. saw
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