A.are used to; polluting | B.is used to; polluting |
C.is used to; polluted | D.is used to; being polluted |
A.joined | B.took part in | C.became | D.were |
A.keep | B.borrowed | C.have kept | D.have lent |
A.make | B.makes | C.will make | D.make |
A.works | B.worked | C.had worked | D.working |
A.had gone | B.has gone | C.has been | D.went |
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