When _____ why he went there,he said he was sent there to be trained for a space flight.  [ ]

A. asking                                      

B. being asked  

C. to ask                                      

D. asked

有载分接开关的电动操动机构在极限位置设有电气限位和机械限位装置。向极限位置以外操作时，（）装置应先起作用。

A、电气限位

B、机械限位

C、声光电

D、跳闸