某混凝土重力坝，正常蓄水位860.50m，校核洪水位862.40m。溢流坝堰顶高程定为850.40m，开敞式溢流堰(上游采用双圆弧曲线、上游堰面坡比为3:2、下游采用WES幂曲线)，溢流堰相对高度65.00m，定型设计水头(H_d)取最大水头(H_max)的85%，堰面曲线参数(  )。

  A．y=0.07861x^1.81、R₁=4.896m、R₂=2.244m

  B．y=0.06945x^1.85、R₁=5.100m、R₂=2.040m

  C．y=0.07411x^1.836、R₁=6.936m、R₂=2.142m

  D．y=0.08806x^1.776、R₁=4.590m、R₂=0.000m