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

[EX Q]: All enzymes have an optimal temperature and ph.
[EX A]: All enzymes have an optimal temperature and what?

[EX Q]: Stirring, surface area, and temperature affect the rate at solute dissolves what occurs.
[EX A]: Stirring, surface area, and temperature affect the rate at which what occurs?

[EX Q]: Leaves export sugar to roots and other nonphotosynthetic parts of the plant through the veins.
[EX A]:
How do leaves export sugar to roots and other nonphotosynthetic parts of the plant?