Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

[EX Q]: All enzymes have an optimal temperature and ph.
[EX A]: All enzymes have an optimal temperature and what?

[EX Q]: If an air mass forms over an ocean it is called a maritime air mass.
[EX A]: If an air mass forms over an ocean it is called what type of air mass?

[EX Q]: When liquid water changes to water vapor it is called evaporation.
[EX A]:
When liquid water changes to water vapor it is called?