A.had done | B.would do | C.was doing | D.did |
A.sat | B.was sitting | C.have sat | D.were sitting |
A.have; polluting | B.has; polluted |
C.has; from being polluted | D.have; being polluted |
A.is | B.were | C.was | D.are |
A.ran | B.was running | C.had run | D.has run |
A.have been teaching | B.was teaching | C.taught | D.had taught |
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