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

Virtually all aquatic organisms depend directly or indirectly on protists for food.
Virtually all aquatic organisms depend directly or indirectly on what for food?

Stirring, surface area, and temperature affect the rate at solute dissolves what occurs.
Stirring, surface area, and temperature affect the rate at which what occurs?

All solutions contain at least two substances.

All solutions contain at least how many substances?