设D由圆r=2围成，则∫∫D√x2+y2dxdy=()

设D由圆r=2围成，则∫∫D√x2+y2dxdy=()
A、8π/3
B、4π
C、(16/3)π
D、π
【正确答案】：C
【题目解析】：∫∫D√x2+y2dxdy=∫02πdθ∫02r•rdr=∫02π(1/3)r3|03=(16/3)π故应选C．