On cold days, a heater is necessary.

Hydrocarbons are fundamental components of organic chemistry.

The wheel of my bicycle has gone flat.

Lithium hydride plays an important role in chemical reactions.

Hydrogen peroxide is often used for disinfecting wounds.

He is a world-renowned bacteriologist.

He is traveling around the world as an ecologist.

He is a world-famous archaeologist.

Aristotle was a famous philosopher in ancient Greece.

His hobby is underwater photography.