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

Mucous does the esophagus produce for lubrication.
What does the esophagus produce for lubrication?

If an air mass forms over an ocean it is called a maritime air mass.
If an air mass forms over an ocean it is called what type of air mass?

Processing of filtrate in the proximal tubule helps maintain the ph level in body fluid.

Processing of filtrate in the proximal tubule helps maintain what level in body fluid?