Edward is collecting data on the average length of lizards from head to tail for a particular generation. Initially, the average length of the lizards was 20 centimeters, and the lizards grew at a relatively fast rate. Two years later, the average length of the lizards was about 22.197 centimeters. With each passing year, the lizards still increased in length, but the growth rate slowed considerably. Which equation in the general form of a natural logarithmic function, f(x)= a In (x - h) + k , represents the average length of lizards in this generation? (Hint: The graph passes through the point (h + 1,k).)