He is an expert in toxicology.

Enokitake is often used in soup.

My grandmother loves tempura made with maitake mushrooms.

Throwing away food scraps is a waste of food.

This restaurant offers an all-you-can-eat service on weekends.

He thinks that war is a necessary evil.

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.