Detailed Instructions: Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
See one example below:
Problem: Earth rotates on its axis once times in one day.
Solution: How many times does Earth rotate on its axis in one day?
Explanation: The given output correctly poses a question based on the scientific fact given.

Problem: The stomach mucosa’s epithelial lining consists only of surface mucus cells, which secrete a protective coat of alkaline mucus.
Solution:
The stomach mucosa’s epithelial lining consists only of surface mucus cells, which secrete a protective coat of what?