They are twin brothers.

This is my twin sister.

She bought a pair of red shoes.

A conic section is a part of geometry, including circles, ellipses, hyperbolas, and parabolas.

He was wearing a cone-shaped hat.

My friend was diagnosed with keratoconus.

Please use the emergency stairs in case of a fire.

Due to the earthquake, the city declared a state of emergency.

Discrete mathematics is an important field that forms the basis of computer science.

He is majoring in applied mathematics at university.