Which of the Following Statements Regarding a Fission Based Nuclear

Which of the following statements regarding a fission based nuclear reactor is not correct?

A) A nuclear fission reactor uses the heat energy released by the fission of U-235 to produce steam.
B) The control rods in a nuclear reactor contain materials which absorb neutrons.
C) The moderator in a fission reactor slows down the neutrons produced from the fission of U-235.
D) (heavy water) ,graphite,and H₂O (light water) have been used as moderators in fission reactors.
E) The uranium dioxide fuel pellets used in a U.S.light-water reactor are made up mostly of the U-235 isotope.