An Object of Mass M Moving at Speed V₀ Strikes

Multiple Choice

An object of mass m moving at speed v₀ strikes an object of mass 2m which had been at rest.The first object bounces backward along its initial path at speed v₀.Is this collision elastic,and if not,what is the change in kinetic energy of the system?

A) The collision is elastic.
B) The kinetic energy decreases by mv².
C) The kinetic energy decreases by mv²/2.
D) The kinetic energy increases by mv².