问题
选择题
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
答案：D
答案选D，可视为once it is begun之省略。
【标签】省略
搜题请搜索小程序“爱下问搜题”
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
答案选D，可视为once it is begun之省略。
【标签】省略
