Water vapor must get warmer. Water vapor must lose heat energy. Precipitation must begin to fall and run off. Transpiration must add water vapor to the atmosphere.
I gave my students this multiple choice question: What must occur before clouds can form?

Only one answer is correct among these 4 choices:
- Water vapor must get warmer.
- Water vapor must lose heat energy.
- Precipitation must begin to fall and run off.
- Transpiration must add water vapor to the atmosphere.

Could you tell me which one is correct?

Water vapor must lose heat energy.