A programmed computer begins to show on its screen the figures you need
A．to be switched on
B．when switched on
C．switching on
D．being switche don
正确答案：B
whenswitchedon是个省略了“itis”的时间状语从句意思是“当它被打开时”A．tobeswitchedon是不定式的被动式不能表示时间；C．switchingon是现在分词表示主动；D．是现在分词的被动式但放在句尾不能表示时间
