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

Câu hỏi :

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      

D that its full extent was realized

* Đáp án

C

* Hướng dẫn giải

Phương pháp giải:

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