E8B09 (A) 
How are the pulses of a pulse-modulated signal usually transmitted?
A. A pulse of relatively short duration is sent; a relatively long period of time separates each pulse
B. A pulse of relatively long duration is sent; a relatively short period of time separates each pulse
C. A group of short pulses are sent in a relatively short period of time; a relatively long period of time separates each group
D. A group of short pulses are sent in a relatively long period of time; a relatively short period of time separates each group
