TASK DEFINITION: Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
PROBLEM: Although they differ vastly in hardness, pencil lead and diamonds both contain carbon.

SOLUTION: Although they differ vastly in hardness, pencil lead and diamonds both contain what element?

PROBLEM: Surface tension is responsible for the fact that small insects can walk on water.

SOLUTION: Surface tension is responsible for the fact that small insects can do this on water?

PROBLEM: Menstrual cycle is the name for a series of changes in the reproductive system of mature females that repeats every month on average.

SOLUTION:
What is the name for a series of changes in the reproductive system of mature females that repeats every month on average?