Prove: If
$$
\mathbf{F}(x, y, z)=f(x, y, z) \mathbf{i}+g(x, y, z) \mathbf{j}+h(x, y, z) \mathbf{k}
$$
is a conservative field and $f, g,$ and $h$ are continuous and have continuous first partial derivatives in a region, then
$$
\frac{\partial f}{\partial y}=\frac{\partial g}{\partial x}, \quad \frac{\partial f}{\partial z}=\frac{\partial h}{\partial x}, \quad \frac{\partial g}{\partial z}=\frac{\partial h}{\partial y}
$$
in the region.