A. should have heard B. must have heard C. might have heard D. could not have heard
A. should have been cleaned B. would have been cleaned C. must have been cleaned D. might have been cleaned
A. understand B. to understand C. understanding D. understood
A. know B. knew C. had known D. have known
A. Continuing B. Continued C. Having continued D. To continue
A. where B. which C. when D. what
A. has kept B. keeps C. keep D. keeping
A. which B. what C. that D. how
A. had been B. were C. was D. am
A. bebuilt B. wouldbebuilt C. werebuilt D. arebuilt
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