That information is completely unnecessary.

He thinks that war is a necessary evil.

It's difficult to adjust the hot and cold in this room.

We use warm salt water to thaw tuna.

His body showed a rejection reaction to the transplanted organ.

His single word triggered a chain reaction, and everything changed.

She overreacted to his words.

Nuclear reactions are used for mass production of energy.

I was surprised by his overreaction.

We played karuta at the New Year's party.