His opinion is very important.

I take supplements every day to supplement vitamins.

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.

We gathered to discuss that issue.

He is supporting that theory.

I can't see an end to the argument with him.

It is important to understand the importance of health.

What is the complement of this sentence?