He is an expert in chemistry.

He is an expert in bibliography and has many publications.

He is very interested in ecology.

He is majoring in agronomy.

He is globally recognized as an expert in epidemiology.

I am majoring in nutrition science at university.

He used a large sum of money for investment.

He used a large amount of money for investment.

He is known as a specialist in historical studies.

He is working hard on his studies every day.