The rate at which a certain disease spreads is proportional to the product of the percentage of the population with the disease and the percentage of the population that does not have the disease. If the constant of proportionality which the disease is spreading is 0.03, and y is the percent of people with the disease, then which of the following equations gives R/(t), the rate at which the disease is spreading?
A. R(t) = 0.03y
B. R(t) = 0.03 dy/dt
C. R(t) = 0.03y(1 - y)
D. dR/dt = 0.03R(1 - R)
E. dR/dt = 0.03R