题目4.(单选题) 设z=u^2+v^2,u=x+y,v=x-y,则(partial z)/(partial x)=A. 4xB. 4yC. 2(x+y)D. 2(x-y)4.(单选题) 设$z=u^{2}+v^{2},u=x+y,v=x-y$,则$\frac{\partial z}{\partial x}=$A. 4xB. 4yC. 2(x+y)D. 2(x-y)题目解答答案A. 4x