The following contour map of function $F(x, y)$ indicates four points: A, B, C, and D. The values to the left of the contour indicate the value of the function for the depicted contour. Answer the questions that follow.
a. Starting at point B, which of the following is the closest approximation of $\frac{\partial F}{\partial x}$ in the direction of increasing $x$?
-20
-10
10
20
b. Starting at point C, which of the following is the closest approximation of $\frac{\partial F}{\partial y}$ in the direction of increasing $y$?
-10
-1/10
1/10
10
