The electrolytic capacitor is an important part of electronic equipment.

There is an old radio cassette in my room.

My grandfather still uses an old transistor radio.

He is operating a radio-controlled helicopter.

The car radio in my car has broken.

There is a new clock radio in my room.

Do you understand the necessity of this project?

That information is unnecessary.

That information is completely unnecessary.

He thinks that war is a necessary evil.