Graph theory is a branch of mathematics that studies mathematical structures called graphs.

He works in the marketing division of the company.

This pie chart shows the company's sales.

We are building a new network system.

The structure of this building is very complex.

This chart shows the increase and decrease in sales.

I love mathematics.

He is conducting research on a new energy source.

He is researching about a new energy source.

He is good at explaining that theory.