TASK DEFINITION: Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
PROBLEM: Unlike ammonia, oxygen cannot be liquefied at room temperature because its critical temperature is below room temperature.

SOLUTION: Unlike ammonia, oxygen cannot be liquefied at room temperature because its what is below room temperature?

PROBLEM: Poles parts of the planet does solar energy have difficulty reaching.

SOLUTION: What parts of the planet does solar energy have difficulty reaching?

PROBLEM: Liquid has a definite volume, but not a definite shape.

SOLUTION:
What state of matter has a definite volume, but not a definite shape?