[单选题]设有平面闭区域D={(x，y)|-α≤x≤α，x≤y≤α)，D1={(x，y)|0≤x≤α，x≤y≤α)，则∫∫D(xy+cosxsiny)dxdy=() A 2∫∫D1cosxsinydzdy B 2∫∫D1xydxdy C ∫∫D1(xy+cosxsiny)dxdy