He is an expert in applied physics.

This orthophoto shows the details of the terrain very clearly.

His father is a very strict person.

During the Yuan dynasty, Chinese culture developed greatly.

This is my original.

Understanding the original principle is important for solving problems.

The budget for this project has been reduced by 20%.

What is the source of this information?

The fountainhead of this river is at the top of the mountain.

Mr. Xi is my best friend.