Martin wants to use coordinate geometry to prove that the opposite sides of
 a rectangle are congruent. He places parallelogram ABCD in the coordinate
 plane so that A is (0.0). B is (a,0). C is (a, b), and D is (0, b). 
 What formula can he use to determine the distance from point D to point A?
 A 10-12 +(0-09 =B=0
 B. -2) = (-0? = VB =D
 C. 0-0j? =(3-03 = 8
 D. (2-2)2+(0-0)2 = 8