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.

The leaves of that tree were dyed red.

I picked up a leaf that was falling in the park.

In this park, there are three beautiful flat leaves.

You need to initialize the computer.

You need to initialize the computer.

It is important to understand the importance of health.

He is an expert in embryology, studying the developmental processes of many kinds of organisms.