40. The professor wrote a book about the keys ___________ the true nature of the universe.
(A) understanding
(B) to understanding
(C) to have understood
(D) of having understood

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統計： A(88), B(179), C(42), D(46), E(0) #860509

詳解 (共 2 筆)

#1452559
key to+ n/ving---答案 
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#1125002
為什麼B?
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