What does the limit as h approaches 0 of (f(x+h,y)-f(x,y))/(h) represent? A. The derivative of f with respect to x at the point (x,y). B. The derivative of f with respect to y at the point (x,y). C. The slope of the tangent line to the curve defined by f at the point (x,y). D. The average rate of change of f with respect to x over a small interval around the point (x,y).