Arisa is my best friend.

He is suffering from a subacute illness.

This species has different characteristics depending on its subgroup.

This airplane flies at subsonic speed.

I learned about the reaction of nitrous acid in chemistry class.

Hypochlorous acid is a hypo compound of chlorine.

He believes in the geocentric theory.

Global warming is a big issue that affects all of us.

A terrestrial planet may have an environment similar to Earth.

He is an expert in geophysics.