Ihave an f in math, i need to get this done, can someone me?

Clearly, it cannot be A or D, since neither of those involve areas. They involved the length of something, whether the perimeter of the circle, or the length of the diameter. It can't be area of a circle either, because when you draw this out, it looks like a slice of cake. That means that the answer would be 

C. Sector of a circle

It cannot be a, b, or d so it has to be c