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

Q: Certain air pollutants form acid liquid when dissolved in water droplets in the air.

A: Certain air pollutants form which liquid when dissolved in water droplets in the air?
****
Q: Lichens are not a single organism, but rather an example of a mutualism.

A: Lichens are not a single organism, but rather an example of a what?
****
Q: The rate of decay of carbon-14 does remains stable over time.

A:
The rate of decay of carbon-14 does what over time?
****