}}}}}(A) an untrained woman should do?

Scream until he tells her to stop. Try to do what he wants until she sees an opportunity to escape. Untrained empty hand against a knife is a VERY bad spot to be in!

}}}}}}(B) What do you think YOU realistically would do?

Trap the weapon as soon as possible, soften him up with rapid strikes to vital areas, and disarm the knife. It ALL depends, of course, on how he's attacking you. If he's dumb enough to stand behind me while holding the knife to my throat, he's getting stabbed in the neck (grab knife hand, hold firmly against your body, drop your weight down as you twist into his body. The knife goes right into the neck). If he sticks the knife in my side, he's getting the knife taken away from him. If he's standing in front of me waving the knife, then out comes my knife and we'll see if he wants to continue at that point. If he does, we'll both get cut, but hopefully my training will see to it that he gets cut a lot worse than I do!

here are my rules for any situation in which I am faced with a non-ranged weapon.

1) Run
2) If for some reason I can't run, hide.
3) If I can't run and I can't hide, find an equalizer.
4) If there's no running, no hiding, and there's absolutely nothing to pick up to use, that's when things are incredibly bad, and I fight empty handed until:
5) As soon as possible, run!

}}}}}(C) What if it were a gun instead of a knife (unlikely in the UK, I know, but possible).

Well I live across the pond in the States, so it's a lot more likely here. If it's a gun and he's standing 15 feet away, I'm pretty much screwed. I'll toss him my wallet if he wants that but if he just wants to kill me, I start running away toward the nearest cover, taking a zigzag path to make it harder to hit me. If he pulls it and sticks it right up to my body (close, in other words) I go for the disarm.