Define Variables and Write the Sentence in Function Notation $\pi$ Times Diameter

Define variables and write the sentence in function notation. The circumference of a circle is a function of the diameter. Circumference is $\pi$ times diameter.

A) $C = \text { circumference, } d = \text { diameter, } C ( d ) = \pi d ^ { 2 }$
B) $C = \text { circumference, } d = \text { diameter, } C ( d ) = \pi d$
C) $C = \text { circumference, } d = \text { diameter, } C ( d ) = \frac { d } { \pi }$
D) $C = \text { circumference, } d = \text { diameter, } C ( d ) = \pi ^ { 2 } d$
E) $C = \text { circumference, } d = \text { diameter, } C ( d ) = \frac { \pi } { d }$