A-A+
A programmed computer begins to show on its sc
问题详情
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
参考答案
正确答案：B
when switched on是个省略了“it is”的时间状语从句，意思是“当它被打开时”。A．to be switched on是不定式的被动式，不能表示时间；C．switching on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。
