A2. Let $\alpha$ and $\beta$ be acute angles in a right triangle that is not isosceles. Then $\sin (\alpha+\beta)$ is equal to:
(A) $-\cos 2 \alpha$
(B) $2 \cos ^{2} \alpha$
(C) $2 \sin ^{2} \beta$
(D) $\sin ^{2} \alpha+\cos ^{2} \beta$
(E) 1
A2. Given $\alpha+\beta=\frac{\pi}{2}$, then $\sin (\alpha+\beta)=1$.