What Role Do the Cadmium Control Rods Play in a Fission

What role do the cadmium control rods play in a fission reactor?

A) The rods control the rate of fission by absorbing neutrons.
B) The cadmium combines with spent uranium fuel to produce a non-radioactive product.
C) The rods focus the neutrons toward the center of the reactor.
D) The cadmium acts as a catalyst,enabling fission to occur at lower temperatures.
E) The rods move forward and backward,driving the pistons that turn the turbines.