已知Z=xf（y/x）+2yg（x/y），其中f，g均为二阶可导函数，求az/ax，a²z/axay？（）

A.f(u)-f'(u)/x+2g'(v);f(u)-f'(u)/x+2g'(v)
B.f(u)-f'(u)/x+3g'(v);f(u)-f'(u)/x+2g'(v)
C.f(u)-f'(u)/x+1g'(v);f(u)-f'(u)/x+2g'(v)
D.f(u)-f'(u)/x+2g'(v);f(u)-f'(u)/x+4g'(v)