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.

I eat delicious cooked grains (rice) every day.

He is an expert in ethology, and his research is highly regarded worldwide.

She has zoophobia, so she can't go to the zoo.