The graphite rods in the nuclear reactor A. react with U to release energy B. produce neutrons C. undergo combustion which triggers the nuclear fission D. convert fast moving neutrons into thermal neutrons

The correct answer is: D. convert fast moving neutrons into thermal neutrons.

Graphite rods are used in nuclear reactors to slow down fast-moving neutrons. This is important because nuclear fission can only occur when neutrons are moving slowly enough to be captured by the uranium-235 nuclei. The graphite rods do this by scattering the neutrons, which causes them to lose energy.

The other options are incorrect. Option A is incorrect because graphite does not react with uranium. Option B is incorrect because graphite does not produce neutrons. Option C is incorrect because graphite does not undergo combustion.

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