*** Posted by Eric T ***
I'm pre-studying to get my private pilot's license. I have some confusion
about some terminology on the Aeronautical chart:

Some airports with a tower have a C symbol next to the CT frequency,
indicating that the frequency is a CTAF when the tower is closed.
But some of these airports also have a different UNICOM frequency.

Why do they have both? Are they used for different things? How do
you know which one to use, and when?