摘要： The research is so designed that once nothing can be done to change it． begun
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the research is so designed that once ____ nothing can be done to change it．
A．begins
B．having begun
C．beginning
D．begun
查看习题详情和答案>>The research is so designed that once ____________ nothing can be done to change it．
A．begins B．having begun C．beginning D．begun
查看习题详情和答案>>
The research is so designed that once ________ nothing can be done to change it．
[ ]
A．begins
B．having begun
C．beginning
D．begun