In the figure, the area of square W X Y Z is 25 \mathrm{~cm}^{2}. The four smaller squares have sides 1 \mathrm{~cm} long, either parallel to or coinciding with the sides of the large square. In \triangle A B C, A B=A C, and when \triangle A B C is folded over side \overline{B C}, point A coincides with O, the center of square W X Y Z. What is the area of \triangle A B C, in square centimeters?
Answer Choices
A. \dfrac{15}{4}
B. \dfrac{21}{4}
C. \dfrac{27}{4}
D. \dfrac{21}{2}
E. \dfrac{27}{2}