8.L为曲线 ^2=x 上点O(0,0)和点B(1,1)的一段-|||-弧,则 (int )_(2)^y(d)_(5)= ()-|||-A dfrac (1)(2)(5sqrt (5)-1)-|||-B dfrac (1)(6)(5sqrt (5)-1)-|||-C dfrac (1)(3)(5sqrt (5)-1)-|||-D dfrac (1)(12)(5sqrt (5)-1)