TASK DEFINITION: Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
PROBLEM: Mucous does the esophagus produce for lubrication.

SOLUTION: What does the esophagus produce for lubrication?

PROBLEM: The seven unique crystal types are defined by faces parts of themselves (parts that intersect at various angles).

SOLUTION: The seven unique crystal types are defined by what parts of themselves (parts that intersect at various angles)?

PROBLEM: When volume does not change, temperature is proportional to pressure.

SOLUTION:
When volume does not change, temperature is proportional to what other property?