I still think it's a parent's job to discuss the subject, but when it comes to the facts about pregnancy, sexually transmitted disease, safe sex and medical and social resources available, I think the school can cover those comprehensively and consistently if given the right tools.
Option 1. prevents kids from learning much of what they should. Option 3. invites them to learn it all... retroactively.
Abstinence is effective, and the only sure fire way to prevent pregnancy and STIs, it's just that all creatures have an overwhelming urge to have sex. However, I agree that 2 is the best way, because abstinence is a conclusion you may reach by considering how sex can affect someone, and you can teach it alone because it builds off of a comprehensive knowledge of sex. Furthermore, it is a choice, and those who don't choose to be abstinent need to know how to protect themselves from STIs and such.
Good parenting! I got the sex talk when my mom was pregnant with my little sister (I was three), and she was anatomically correct and factual. I think that was a great way to do it. I didn't feel weirded out and my three-year-old curiosity about where babies came from was satisfied. I've been the same way with my kids. I think if you are secretive and misleading and uncomfortable, that transfers to your children's current and future beliefs (and emotions) regarding sex.