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.

Fact: producing thrust causes something to move.
engines produce thrust.

Fact: a watch is used for measuring time.
measuring time hours.

Fact: Some viruses have an envelope of phospholipids and proteins.

envelope phospholipids and proteins.