In the Drake Equation (Number of Civilizations = NHP ×

In the Drake equation (Number of Civilizations = NHP × f_life × f_civ × f_now , what do we mean by f_ now?

A) The fraction of planets with civilizations at the present time (as opposed to only in the past or future)
B) The fraction of planets in the galaxy on which a civilization could theoretically develop right now
C) The fraction of civilizations in the universe that currently are sending messages to us
D) The fraction of all species ever to exist that we currently are aware of