In What Way Does the Drake Equation Combine the Various

Multiple Choice

In what way does the Drake equation combine the various factors (e.g. ,fraction of stars with planets,fraction of planets that can support life,etc. ) in an attempt to determine the probability of life existing elsewhere in the Galaxy?

A) It takes the product of all the factors.
B) It takes the sum of each of the factors.
C) It divides the sum of three factors by the sum of the other four factors.
D) It subtracts the sum of six factors from the initial factor,the rate of solar-type star formation.