True-False Determine whether the statement is true or false. Explain your answer. (In Exercises $16-18$, assume that $C$ is a simple, smooth, closed curve, oriented counterclockwise.) If
$$
\int_{C} f(x, y) d x+g(x, y) d y=0
$$
then $\partial g / \partial x=\partial f / \partial y$ at all points in the region bounded by $C$.