21.
(A) was
(B) were
(C) has been
(D) had been

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統計： A(14), B(35), C(9), D(13), E(0) #2450826

詳解 (共 2 筆)

#4496379
答案a前面 astronomers ha...
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#4870938

答案應該是B 

這是與現在事實相反的假設語氣

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