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

Stringed instruments can help show the relationship between tension and frequencies in strings.
Stringed instruments can help show the relationship between tension and what in strings?

Bacteria may divide several times an hour.
Bacteria may divide several what an hour?

Genetic equilibrium occurs evolution what process doesn't exist within the population.
Genetic equilibrium occurs when what process doesn't exist within the population?