What Distinguishes the Defense of Self-Defense from the Defense of Necessity

What distinguishes the defense of self-defense from the defense of necessity?

A) Necessity occurs when an individual must harm an aggressor to ward off an attack. For self-defense, this is not the case.
B) Necessity occurs when an offender has an incompetent attorney. For self-defense, this is not the case.
C) Necessity occurs when an offender is tricked into committing a crime. For self-defense, this is not the case.
D) Necessity occurs when offenders must break the law in order to save themselves or prevent some greater harm. For self-defense, this is not the case.
E) Necessity and self-defense are the same thing.