I used a gas burner in a chemistry experiment.

In mathematics, the commutative law applies to addition and multiplication.

Let's exchange keys tomorrow.

We write in the exchange diary every day.

We wrote essays for peer grading.

He works at the switchboard.

Looking at that person's behavior, I feel like they have some secret.

The police used tear gas against the demonstrators.

Fergus is my best friend.

This factory has significantly reduced its carbon dioxide emissions.