10.《九章算术》中的"商功"篇主要讲述了以立体几何为主的各种形体体积的计算,其中堑堵是指底面为直-|||-角三角形的直棱柱如图,在堑堵 -(A)_(1)(B)_(1)(C)_(1) 中,M是A1C1的中点, =2A(A)_(1)=2AC . dfrac (MN)(BN)=dfrac (1)(3)B(B)_(1)-|||-overrightarrow (MG)=3overrightarrow (GN) 若 =xA(A)_(1)+yAB+zAC 则 x+y+z= ()-|||-__-|||-C1-|||-C M-|||-1-|||-A1 G-|||-->B1-|||-V-|||-A B-|||-9-|||-A. dfrac (7)(8) B. dfrac (9)(8) C. dfrac (11)(8) D. dfrac (13)(8)