the area in the first quadrant bounded by the curves with parametric equations $\displaystyle x=2atan(\theta)$ and $\displaystyle y=2acos^2(\theta)$, and the lines x=0 and x=2a, is equal to

(A) $\displaystyle \pi a^2$

(B) $\displaystyle 2 \pi a^2$

(C) $\displaystyle \frac{\pi a}{4}$

(D) $\displaystyle \frac{\pi a}{2}$

(E) none of these