设函数 $f(x, y)$ 连续, 则二次积分 $\int_{\frac{\pi}{2}}^\pi d x \int_{\sin x}^1 f(x, y) d y$ 等于
A. $\int_0^1 d y \int_{\pi+\arcsin y}^\pi f(x, y) d x$.
B. $\int_0^1 d y \int_{\pi-\arcsin y}^\pi f(x, y) d x$.
C. $\int_0^1 d y \int_{\frac{\pi}{2}}^{x+\arcsin y} f(x, y) d x$.
D. $\int_0^1 d y \int_{\frac{\pi}{2}}^{\pi a r c s i n y} f(x, y) d x$.