The part of the sentence that answers this question is called the complete subject of the sentence. The part of the sentence that answers this question is called the complete predicate of the sentence.
Snowflakes are a form of winter precipitation .
The sun heats the surface of bodies of water. Warm air rises because it is lighter than cold air. Water droplets are tiny drops of water. An example of water vapor is steam. The water vapor that rises from the surfaces of bodies of water mixes with air and rises up into the sky.