A programmed computer begins to show on its screen the figures you need
- Ato be switched on
- Bwhen switched on
- Cswitching on
- Dbeing switche don
搜答案，更轻松！
A programmed computer begins to show on its screen the figures you need
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。