Question ID:PT2 S4 Q16 Passage:Nuclear fusion is a process whereby the nuclei of atoms are joined, or “fused,” and in which energy is released. One of the by-products of fusion is helium-4 gas. A recent fusion experiment was conducted using “heavy” water contained in a sealed flask. The flask was, in turn, contained in an air-filled chamber designed to eliminate extraneous vibration. After the experiment, a measurable amount of helium-4 gas was found in the air of the chamber. The experimenters cited this evidence in support of their conclusion that fusion had been achieved. Stem:Which one of the following, if true, would cast doubt on the experimenters’ conclusion? Correct Answer Choice:CChoice A:Helium-4 was not the only gas found in the experiment chamber. Choice B:When fusion is achieved, it normally produces several by-products, including tritium and gamma rays. Choice C:The amount of helium-4 found in the chamber’s air did not exceed the amount of helium-4 that is found in ordinary air. Choice D:Helium-4 gas rapidly breaks down, forming ordinary helium gas after a few hours. Choice E:Nuclear fusion reactions are characterized by the release of large amounts of heat.