In parallelogram ABCD, ∠A and ∠B are adjacent. The measure of ∠B is twice the measure of ∠A. Which equation gives the exact measure of ∠A?
A. m ∠A + m ∠B = 180°
B.m ∠A + 2 • m ∠A = 180°
C.m ∠A + m ∠B = 90
D.m ∠A + 2 • m ∠A = 90°