13.(单选题,5.0分)-|||-多项式 ((x)_(1),(x)_(2),(x)_(3))=(({x)_(1)+(x)_(2))}^2+(({x)_(1)+(x)_(3))}^2-4(({x)_(2)-(x)_(3))}^2 的标准形为() ()-|||-A .({y)_(1)}^2+({y)_(2)}^2-|||-B .({y)_(1)}^2-({y)_(2)}^2-|||-C .({y)_(1)}^2+({y)_(2)}^2-4({y)_(3)}^2-|||-D .({y)_(1)}^2+({y)_(2)}^2-({y)_(3)}^2