Why is one side of the moon called "the dark side of the moon"?

A the moon's rotation time is exactly the time of its revolution

B the moon's rotation time is exactly twice the time of it's revolution

C the moon's rotation and revolution take the same time

' A ' and ' C ' both say the same thing, and both are correct statements. But they're not a reason to call any part of the moon a "dark side". No part of the moon is dark for more than 2 weeks at a time, and the only reason to talk about a "dark side" of it is ignorance.