Mr. Tani is my best friend.

This valley is a wetland with a rich ecosystem.

We took a walk in the beautiful valley over the weekend.

You saw that guy at the party yesterday, didn't you?

That guy is really smart.

I am very interested in natural science.

Natural numbers start from 0 and continue as 1, 2, 3, 4, 5, 6, 7, 8, 9.

Natural selection plays an important role in the evolution of organisms.

I was moved by the beauty of nature.

Calculating the natural logarithm is an important part of mathematics.