Not until Kentucky\'s Mammoth Cave had been completely explored in 1972 _____.
(A) when was its full extent realized
(B) that its full extent realized
(C) was its full extent realized
(D) the realization of its full extent

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統計： A(11), B(48), C(137), D(15), E(0) #85553

陳琪徨

B1 · 2011/07/28

#202985

Not until Kentucky\'s Mammoth Cave had been completely explored in 1972 _____.

not until 子句放句首，主句要倒裝，故選(C)

未變化前基本寫法為

The full extent of Kentucky\'s Mammoth Cave wasn\'t realized until it had been completely explored in 1972.

或者為

It was not until Kentucky\'s Mammoth Cave had been completely explored in 1972 that its full extent was realized.