Well, in the U.S textbooks, we use a system of 6 kingoms while in other textbooks like Great Britain, they have 5. (Britain isn't the only place with 5)
A Directly, more
I just answered this question on USATEST PREP and got it right.
The difference between analog and digital signals is that an analog signal is a continuous electrical message while digital is a series of values that represent information. Analog is conveyed by electrical current variations.