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

[EX Q]: The correct order of food traveling through the digestive system after it is swallowed is: esophagus, stomach, small intestine, large intestine.
[EX A]: Which list gives the correct order of food traveling through the digestive system after it is swallowed?

[EX Q]: The second step in eukaryotic cell division is division of nucleus part of the cell.
[EX A]: The second step in eukaryotic cell division is division of which part of the cell?

[EX Q]: Mutation is essential in order for evolution to occur because it increases genetic variation and the potential for individuals to differ.
[EX A]:
What phenomenon is essential in order for evolution to occur because it increases genetic variation and the potential for individuals to differ?