Write the Specified Quantity as a Function of the Specified $A = r$

Multiple Choice

Write the specified quantity as a function of the specified variable.
-A square is inscribed in a circle. Write the area of the square as a function of the radius.

A) $A = r$
B) $A = 2 r$
C) $\mathrm { A } = 2 \mathrm { r } ^ { 2 }$
D) $A = 4 r ^ { 2 }$