TASK DEFINITION: Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
PROBLEM: A collapsing nebula leads to nuclear fusion process.

SOLUTION: A collapsing nebula leads to what process?

PROBLEM: If two populations do not mate and produce fertile offspring, separate species result.

SOLUTION: If two populations do not mate and produce fertile offspring, what results?

PROBLEM: Many glasses eventually crystallize, rendering them brittle and this?

SOLUTION:
Many glasses eventually crystallize, rendering them brittle and this?