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

[EX Q]: The ability of matter to combine chemically with other substances is known as reactivity.
[EX A]: The ability of matter to combine chemically with other substances is known as?

[EX Q]: Pressure and vibration are examples of physical type of stimuli.
[EX A]: Pressure and vibration are examples of what type of stimuli?

[EX Q]: Ice wedging occurs because water expands.
[EX A]:
Why does ice wedging occur?