Find the Formula for the Function $A = 2 \pi r$

Multiple Choice

Find the formula for the function.
-Express the area of a circle as a function of its radius r.

A) $A = 2 \pi r$
B) $A = \pi r ^ { 2 }$
C) $\mathrm { A } = \pi \mathrm { r }$
D) $A = \pi r ^ { 3 }$