This one. You don't owe people an explanation of your life. If that confuses them, it's their job to deal with their confusion, not yours.

It took me a while to learn to just say "I don't have a father" if people asked me about my parents, rather than getting into a much more complicated explanation. But socially, that's true, and "socially" is generally all that's relevant when it comes to family. So-called biological relationships usually seem to get used as a tool by people who want to tell you that you aren't real. Why give them the weapon?