题目内容
(经典回放)The research is so designed that once ________ nothing can be done to change it.
[ ]
A.begins
B.having begun
C.beginning
D.begun
答案:D
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题目内容
(经典回放)The research is so designed that once ________ nothing can be done to change it.
A.begins
B.having begun
C.beginning
D.begun