14 单选(4分)下列偏导数计算错误的是 () .-|||-A.-|||-==((x)^2+(y)^2)(e)^x 则 _(x)=2x(e)^x+((x)^2+(y)^2)(e)^x-|||-B. ==((x)^2+(y)^2)ln xy 则 _(1)=2xln xy+x+dfrac ({y)^2}(x)-|||-C. =ln (x+sqrt ({x)^2+(y)^2}), 则 dfrac (partial z)(partial x)|(0,2)=dfrac (1)(sqrt {{x)^2+(y)^2}}-|||-D. (x,y)=(x)^2(y)^3, 则 dfrac (partial f)(partial x)=2x(y)^3