He is an expert in hydrology and is conducting research on flood prevention.

He is an expert in hydrology, and his research is highly valued around the world.

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.

My father owns five boats.

There is a large weir in this river.

I am planning to go to Seki City in Gifu Prefecture next week.

He always remains calm.

He can always maintain calmness.