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

Elements are pure substances that make up all matter.
Elements are pure substances that make up what?

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

An infection may be intracellular or extracellular, depending on this?
An infection may be intracellular or extracellular, depending on this?