In math class, we learned about the concept of union sets.

He is learning how to use collective nouns.

In mathematics, an empty set refers to a set that does not contain any elements.

A power set is a set consisting of all subsets of a set.

There is a communal letterbox in our apartment.

He drew his bow aiming at the target.

He drew his bow aiming at the target.

What is that target?

He is my biggest enemy.

His advice was very practical.