Not until Kentucky’s Mammoth Cave had been completely explored in 1972_________
17/50
Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions. 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.