2.[单选题]-|||-设∑为锥面 =sqrt ({x)^2+(y)^2}(0leqslant zleqslant h) 的外侧,-|||-cosα,cos β,cosy是2在点(x,y,z)处法向量的方-|||-iint ((x)^2cos alpha +(y)^2cos beta +(z)^2cos gamma )ds=-|||-向余弦,则-|||-()()-|||-○ A. -dfrac (1)(2)(pi {n)^4}-|||-bigcirc B. dfrac (1)(2)(pi h)^4-|||-bigcirc C. -dfrac (3)(2)pi (n)^4-|||-bigcirc D.0