His feature story opens and closes with descriptions of two new reports, each _____ one major point in contrast with the other.
How this kind of plant can be ____ in a special way is still unknown to us.
If I ___ free tonight, I'll go to the cinema with you.
Edison had built a chemical lab of ___ when he was very young.
This is the only one of the books on space ___.
---Please help me, will you? ---_____.