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

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

His role is to fulfill his responsibilities as a leader.

It is important to understand the importance of health.

She overreacted to his words.

Nuclear reactions are used for mass production of energy.

His single word triggered a chain reaction, and everything changed.

I was surprised by his overreaction.

His body showed a rejection reaction to the transplanted organ.

He is dedicated to the study of immunochemistry.