Which of the following describes the set of values of a for which the curves x^{2}+y^{2}=a^{2} and y=x^{2}-a in the real x y-plane intersect at exactly 3 points?

**Answer Choices**

A. a=\dfrac{1}{4}

B. \dfrac{1}{4}<a<\dfrac{1}{2}

C. a>\dfrac{1}{4}

D. a=\dfrac{1}{2}

E. a>\dfrac{1}{2}