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.

We need moderate exercise to maintain our health.

Please put the book on the shelf above.

In addition, he can play the piano.

Health is very important.

His opinion is very important.

I was amazed at his extraordinary talent.

Please press this button in case of emergency.