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

[Q]: A change of season and less food usually cause certain animals to migrate.
[A]: Which two environmental changes usually cause certain animals to migrate?


[Q]: Sexual reproduction, in general, relies on sets of cells that are precursors for eggs and sperm.
[A]: What kind of reproduction, in general, relies on sets of cells that are precursors for eggs and sperm?


[Q]: The ph scale is used to succinctly communicate the acidity or basicity of a solution.
[A]:
What scale is used to succinctly communicate the acidity or basicity of a solution?