He is good at playing Beethoven's concertos.

He is good at performing opera.

We have entered a new stage.

The sinusoid is used to represent many phenomena in nature.

He is good at playing Beethoven's variations.

What is your area code?

The limit of this plan is the lack of funds.

Polar bears live in extremely cold areas.

He is improving his piano skills by playing etudes every day.

He always acts without questioning right and wrong.