15000 bài tập tách từ đề thi thử môn Tiếng Anh có đáp án (Phần 57)
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Not until Kentucky’s Mammoth Cave had been completely explored in 1972_________ A. when was its full extent realized B. the realization of its full extent C. was its full extent realized

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Not until Kentucky’s Mammoth Cave had been completely explored in 1972_________

when was its full extent realized

the realization of its full extent

was its full extent realized

that its full extent was realized

Giải thích

Đáp án C

– cấu trúc Not until + N/mệnh đề, mệnh đề đảo: không cho đến tận khi.