At each lattice point in a slope field for the differential equation dxdy=f(x,y), a short line segment is drawn. What does the direction (tilt) of this segment represent?
a) the average rate of change of y over a unit interval starting at the point
b) the exact value of y at that point
c) the slope of the solution curve passing through the point
d) the concavity of the solution curve at the point