An Elastic Collision Is Best Defined as What

An elastic collision is best defined as what?

A) When kinetic energy is conserved before and after the collision.
B) The two colliding bodies have conserved momentum, and stick together at the collision point.
C) Potential energy is conserved before and after the collision.
D) Sound or heat is generated during the collision.
E) The colliding bodies are stretchy in nature and conserve their momentum.