instruction:
In this task, you need to write a topic word from the given fact. The topic word must have at least one word overlap with the given fact. The topic word often involves adding a new word from a related concept. In your topic word, use at least one word from the given fact. Topic words with two or more words work best.
question:
Fact: telephones are used for communication by two people by transmitting sound.
answer:
Sound is waves.


question:
Fact: treating water is used to remove harmful substances before drinking.
answer:
boiling water treat.


question:
Fact: Dilation occurs when cell walls relax.
answer:

Dilation occurs when cell walls relax.