Proof by Smallest Counterexample and Induction - Lecture 11 (Discrete Math)

What does the Well-Ordering Principle state?

1. A.Every non-empty subset of the integers has a least element.
2. B.Every non-empty subset of the natural numbers has a least element.
3. C.Every bounded subset of the rationals has a least element.
4. D.Every non-empty subset of the natural numbers has a greatest element.