Given a fact, create a question that can be answered using the fact. Construct the question such that it is unambiguous, has a unique answer and the answer can be given using the fact.

Fact: freezing point means temperature below which a liquid freezes
If you want to walk over a lake, which of these is necessary?

Fact: a camera is used for recording images
Which would you use to record a live basketball game?

Fact: humidity is the amount of water vapor in the air

Humidity is the amount of what vapor in the air?