Ecology is a field of study that investigates the interrelationships of organisms in the natural world.

He is an expert in medicine.

He is learning the basics of elementary learning.

He clenched his lower jaw tightly to endure the pain.

Epidemiology is the science that studies the occurrence and spread of diseases.

I am majoring in political science at university.

I am majoring in physiology at university.

He is in the third year of junior high school, or in other words, he is in the 9th grade in school years.

He likes going to chamber music concerts.

He is majoring in agronomy at university.