An Aluminum Rod Is 20 $^{\circ}$ CThe Coefficient of Linear Expansion of Aluminum Is 23

An aluminum rod is 20.0 cm in length,has a diameter of 10.0 mm and is at a temperature of 20 $^{\circ}$ C.The coefficient of linear expansion of aluminum is 23.0 $\times$ 10^-6/ $^{\circ}$ C.If the temperature changes to 50 $^{\circ}$ C,then the increase in diameter of the aluminum rod is

A) 4.0 $\times$ 10^-3 mm.
B) 4.9 $\times$ 10^-3 mm.
C) 5.6 $\times$ 10^-3 mm.
D) 6.0 $\times$ 10^-3 mm.
E) 6.9 $\times$ 10^-3 mm.