His carelessness caused the accident.

Do you understand the necessity of this project?

That information is unnecessary.

That information is completely unnecessary.

He was paying attention to the teacher's talk during the class.

He thinks that war is a necessary evil.

This issue requires attention.

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

The government declared a state of emergency to prevent the spread of the new coronavirus.

Nitrous oxide, also known as laughing gas, is used for anesthesia.