is certain is the mystery of Stonehenge has never been fully explained.A. It thatB. Wha

问题补充：

is certain is the mystery of Stonehenge has never been fully explained.

A. It, that

B. What, what

C. It, what

D. What, that

答案：

A. It, that

B. What, what

C. It, what

(答案→)D. What, that

解析：考查名词性从句。本题第一空what引导的是主语从句what is certain，在句中做主语。第二空that引导的是表语从句，that在表语从句中不充当任何成分，只起引导的作用。句意：确定的事情是巨石阵的秘密到现在为止还没有被完全解释。故D正确。故D正确。