In a Certain Nuclear Reactor, Neutrons Suddenly Collide with Deuterons

Multiple Choice

In a certain nuclear reactor, neutrons suddenly collide with deuterons, which have twice the mass of neutrons. In a head-on elastic collision with a stationary deuteron, what fraction of the initial
Kinetic energy of a neutron is transferred to the deuteron?

A) 3/4
B) 8/9
C) 1/2
D) 1/3
E) 5/6