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 am hesitating between 4 options to answer the following question, which option should I choose?
Question: What must occur before clouds can form?
Possibilities:
- 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.

Water vapor must lose heat energy.