设D:x2+y2≤a2,当a____时,∫∫D√(a2-x2-y2)dxdy=π()

设D:x2+y2≤a2,当a____时,∫∫D√(a2-x2-y2)dxdy=π()
A、1
B、3√(3/2)
C、3√(3/4)
D、3√(1/2)
【正确答案】:B