The ideas that signals are costly in general, that a signal may be in flux within a particular population, or that any given signal might be perceived by different receivers, some of which have the same and some of which have different goals as the sender, have been offered as explanations for why

A) dishonest signals will inevitably become predominant throughout a population.
B) only honest signals can be maintained within a population.
C) the terms "honest" and "dishonest" really don't apply within the context of animal communication.
D) we see populations with both honest and dishonest signals.