Girls ALMOST NEVER answer the phone when they see a number that is calling for the first time, unless she knows who it is AND her interest level is already very high before giving out her number.
They always screen their calls, can you imagine them asnwering, calling back, having a boring conversation, etc., with every guy who wants to talk to them. This is true specially of hotties who give out their number to a lot of guys they meet. It is a lot easier to just screen a call, and not call back, than to reject the guy on the spot.
And the correct answer is...........................drum roll please!........................
a. Leave a voicemail.
No voice mail = almost always no call back, unless she doesn't get many calls and she legitimately missed it and she is curious to know who called.
Leave a funny message that will remind her who you are. She probably won't remember you, unless you really qualified this lead, and there was a high interest from her part.
If she just gave you the number and you didn't really connect with her when you got it, then still leave a message, and make sure you say something interesting, that way if she doesn't know who you are, you still come across as someone who is fun and interesting and she would like to get to know.