His opinion is always rational.

He is serving as the president's guard.

He drew a pentagon on the blackboard.

Metalinguistics is an important concept in linguistics.

In this project, it is necessary to combine various data.

It's difficult to remember new words.

She is an expert in nursing.

He is always condemning others with abusive language.

He is a rationalist, making all decisions based on logic and facts.

I am surprised at the irrationality of this system.