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

Limestone is insoluble in water, so acid can dissolve it.
Limestone is insoluble in water, so what can dissolve it?

Chemical digestion mainly occurs in the small intestine.
Where does chemical digestion mainly occur?

Krebs cycle is part of cellular respiration and makes atp and naph.
What cycle is part of cellular respiration and makes atp and naph?