Heliocentrism is the theory that the sun is the center of the universe.

Nitrogen dioxide is a cause of air pollution.

The Turkic language family is a group of languages spread across Central Asia and Siberia.

He moved ferociously like a lion.

He got a new watch.

He was observing the birds.

In physics, a meson is a type of particle made up of a quark and an antiquark.

My younger brother is the middle child in our family.

When he was a middle-school student, he used to study in the library every day.

He was always by my side as my helper.