One way to define communication is as something that happens when a sender produces a signal that contains information that is transmitted through the environment, that is then detected by a receiver, who then interprets the signal and decides how to respond. This sort of definition may create some problems because it may inappropriately include the transmission of information that might more appropriately be described as a

Many believe that a definition of communication must include

A signal transmitted literally at the speed of light would have to be a _____ signal.