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 |
A.knew | B.had known | C.have known | D.have been knowr |
A.think | B.thought | C.have thought | D.am thinking |
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