In Principle, the Drake Equation Should Enable Us to Calculate

Multiple Choice

In principle, the Drake equation should enable us to calculate the exact number of intelligent civilizations capable of interstellar communication in our galaxy right now. However, currently this is not feasible because

A) we do not have precise values for any of the factors in the equation
B) it is impossible for us to ever know the precise values of any of the factors
C) we have precise values for the first three factors, but not the last factor
D) we have a precise values for the first factor, but not for any of the other factors