42. Correct. The answer is true. Write S_t = S₀e^rt in the natural log form: lnS_t = lnS₀ + lne^rt = lnS₀ + rt. Therefore, d(lnS_t)/dt= r. In general, the rate of growth of y = f(x) is defined as r_y =[dy/dt]/y = marginal function/total function = d(lny)/dt.