His behavior feels uncertain.

I feel uneasy about his attitude, I have no idea what he's thinking.

He ate one apple.

He is majoring in statistics.

It is important for each person to fulfill their role.

He has a very passive personality.

Quantum mechanics is a branch of physics that studies the behavior of microscopic particles.

He is studying thermodynamics in depth.

He is an expert in analytical mechanics and deeply understands its theory.

He is an expert in electrodynamics.