累次积分∫0^n/2 dθ∫0^cosθf(rcosθ,rsinxθ)rdr可以写成【 】.
A、∫0^1dy∫0^√y-y^2 f(x,y)dx
B、∫0^1dy∫0^√1-y^2 f(x,y)dx
C、∫0^1dy∫0^1 f(x,y)dy
D、∫0^1dy∫0^√x-x^2 f(x,y)dy