Neutrons Produced in the Fission of Uranium Are Rapidly Moving

Multiple Choice

Neutrons produced in the fission of uranium are rapidly moving projectiles and must be slowed before they can produce more fission.If the neutrons collide elastically,hydrogen is effective in slowing them down because

A) hydrogen atoms repel neutrons.
B) a hydrogen atom is much more massive than a neutron.
C) a hydrogen atom and a neutron have about the same mass.
D) a neutron is much more massive than a hydrogen atom.
E) hydrogen atoms attract neutrons.