The conditions necessary for the formation of cumulonimbus clouds are a lifting action and
A.	unstable, moist air.
B.	either stable or unstable air.
C.	unstable air containing an excess of condensation nuclei.

Answer (C) is incorrect.
There must be moisture available to produce the clouds and rain; e.g., in a hot, dry dust storm, there would be no thunderstorm.


Lifting action, unstable air, and moisture are the ingredients for forming cumulonimbus clouds.