He is an expert in geophysics.

He is a world-renowned biologist.

He is a world-renowned zoologist.

It's difficult to understand the principles of electrooptics.

I am majoring in econometrics at university.

He was deeply grieving the death of his family.

My collection is finally complete.

Let's calculate so that all numbers become equal.

He taught me Japanese.

Various types of plants are planted in my garden.