In mathematics, equivalence classes are a very important concept.

It's very easy to walk on this flat road.

The initial response when an earthquake occurs is very important.

My brother is a master of Taido.

We belong to the same class.

This statue is made of copper.

He found an old copper coin.

Carbonated beverages often go well with meals.

I organized the data using a spreadsheet software.

Nitrous oxide can be used for anesthesia and to boost engine power.