My hobby is playing the koto.

He is studying the history of Tonkin.

He is an expert in chemistry.

He received the letter challenging him to a duel and began preparing for the duel.

He complained about the pain in his balls.

Gender roles are an important element in defining individual behavior in society.

His role is to fulfill his responsibilities as a leader.

Organic solvents play an important role in chemical reactions.

It is important to understand the importance of health.

Aldaric acid is a compound produced by the oxidation of sugars.