The nitrogen cycle is very important for maintaining ecosystems on Earth.

The ecosystem of this lake is very fragile.

We always pay attention to the maintenance of this machine.

Please put the book on the shelf above.

In addition, he can play the piano.

We need moderate exercise to maintain our health.

His opinion is very important.

Health is very important.

I was amazed at his extraordinary talent.

Nitrogen makes up about 78% of the Earth's atmosphere.