In the figure, triangle ABC is congruent to triangle ADC . If the square ABCD is dilated by a factor of 2 to form A'B'C'D', what is the ratio of the area of A'B'C'D' to the area of ABCD?

a.) 2 : 1

b.) 3 : 1

c.) 4 : 1

d.) 5 : 1