Electronic signal

I'm thinking that the answer for this question is either A or B but I need someone else's opinion on this. Which one of the following signals is in common use in electronics today? A. continuous d.c.
B. constant amplitude a.c
C. Interrupted a.c.
I know that continuous d.c is a voltage but could it be considered a signal too? Thank you......

If the definition of a signal is the something that transfers information then only one of the three selections is the correct answer.

Think information delivery, not power delivery.

Think about this, too:

The first two choices could transmit information. However, the only data they could convey would be 1 bit of binary information (that is, either the presence or absence of the DC or AC current). Not very useful as a signal.