Option b involves not using OPK at all. dh and I are doing this. We are BD on CD5, 9, 13, and 17. I usually ovulate around CD14, but with this method I'm not doing OPK so I'm not stressing about timing.
Option C involves every 4 days plus another attempt at positive OPK. So if dh and I BD on CD9 and then got a positive on CD11 we would BD again even if it had not been 4 days. This isn't as good of a pink sway but does Increase odds of conception.