_____ deep down in the earth, the dead forests rotted away and became coal.

--Can you tell me ______ I can do with the broken computer?-- Sorry, you’d better ask an expert ______ to deal with it.

A person , when_________，can often do what is normally beyond his ability.

We all think that the plan you suggest _____ the work is very practical．

In order not to be disturbed ,I spent three days __________ in my study.