(3)若二元函数 z=f(x,y) 在点P0(x0,y0 )处的两个偏导数 dfrac (partial z)(partial x) dfrac (partial z)(partial y) 存在,则 ()-|||-(A)f(x,y)在P0点连续; (B) =f((x)_(1),(y)_(0)) 在P0点连续;-|||-(C) =dfrac (partial z)(partial x)(int )_({p)_(0)}dx+dfrac (partial z)(partial y)(|)_({p)_(0)}^1}(d)_({p)_(0)}^d . (D)A,B,C都不对.