How do I know if I am registered with Selective Service?

I am currently filling out an application for a science research grant from the Department of Defense. In the online application, it asks me the following question:

Are you registered with Selective Service?
- Yes
- No
- I am not required to register

As far as I know, any of the above could be the answer! I just have no idea, nor do I know how the average person would know this.

I am a 22-year-old female US citizen who was born in the United States. I have never had any sort of affiliation with the military.

Am I automatically registered, as a citizen?
Am I not registered, if I never did register?
Am I not required to register?

?????

Please help!