A.has | B.have | C.are | D.was |
A.have been | B.has | C.had been | D.have |
A.are | B.is | C.were | D.was |
A.are | B.were | C.be | D.is |
A.are difficult | B.has proved difficult |
C.is supposed difficult | D.have been found difficult |
A.are | B.were | C.is | D.was |
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