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

Do particles collide more in two reactants fluid they are both in fluid forms or solid forms.
Do particles collide more in two reactants when they are both in fluid forms or solid forms?

A bow wake is created when the wave source moves faster than the wave propagation speed.
What is created when the wave source moves faster than the wave propagation speed?

The immune system typically recognizes, attacks, and destroys foreign cells or substances that may cause disease.

Which body system typically recognizes, attacks, and destroys foreign cells or substances that may cause disease?