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

[EX Q]: Chemical digestion mainly occurs in the small intestine.
[EX A]: Where does chemical digestion mainly occur?

[EX Q]: The sun and the moon appear to be about the same size in the sky because the moon is smaller in diameter and is closer to earth than the sun.
[EX A]: Which statement best explains why the Sun and the Moon appear to be about the same size in the sky?

[EX Q]: Soluble minerals and clays accumulate in subsoil soil layer, allowing it to hold more water.
[EX A]:
Soluble minerals and clays accumulate in what soil layer, allowing it to hold more water?