I am half color blind, but is there a green tone in the third one? I would get rid of it. I'm sure the people who judge your photos prefer normal skintones. More like the first one. Blue skintones often look good as well, but normal is often best. But the third one is by far the best shot. Strong portrait, good lighting, beautiful model. The second best is the one with the ring.

The other three I don't like so much. First one is a bad angle IMO. It doesn't feel right. Instead of that, I would go with a full body shot to show that I (you) am capable of more than just close up portraits!
Second one has a boring angle as well. You could do something more interesting with the same subject. Think about it.
Last one is pretty good, it's just too dark and too similar to the other ones.

Good luck with the assignment.