16. 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.
Which one of the following, if true, would cast doubt on the experimenters’ conclusion?
(A) Helium-4 was not the only gas found in the experiment chamber.
(B) When fusion is achieved, it normally produces several by-products, including tritium and gamma rays.
(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.
(D) Helium-4 gas rapidly breaks down, forming ordinary helium gas after a few hours.（C）
(E) Nuclear fusion reactions are characterized by the release of large amounts of heat.
17. Every photograph, because it involves the light rays that something emits hitting film, must in some obvious sense be true. But because it could always have been made to show things differently than it does, it cannot express the whole truth and, in that sense, is false. Therefore, nothing can ever be definitively proved with a photograph.
Which one of the following is an assumption that would permit the conclusion above to be properly drawn?
(A) Whatever is false in the sense that it cannot express the whole truth cannot furnish definitive proof.
(B) The whole truth cannot be known.
(C) It is not possible to determine the truthfulness of a photograph in any sense.
(D) It is possible to use a photograph as corroborative evidence if there is additional evidence establishing the truth about the scene photographed.（A）
(E) If something is being photographed, then it is possible to prove definitively the truth about it.
Questions 18-19
Some cleaning fluids, synthetic carpets, wall paneling, and other products release toxins, such as formaldehyde and benzene, into the household air supply. This is not a problem in well-ventilated houses, but it is a problem in houses that are so well insulated that they trap toxins as well as heat. Recent tests, however, demonstrate that houseplants remove some household toxins from the air and thereby eliminate their danger. In one test, 20 large plants eliminated formaldehyde from a small, well-insulated house.
18. Assume that a person who lives in a small, well-insulated house that contains toxin-releasing products places houseplants, such as those tested, in the house. Which one of the following can be expected as a result?
(A) There will no longer be any need to ventilate the house.
(B) The concentration of toxins in the household air supply will remain the same.
(C) The house will be warm and have a safe air supply.
(D) If there is formaldehyde in the household air supply, its level will decrease.（D）
(E) If formaldehyde and benzene are being released into the household air supply, the quantities released of each will decrease.
19. The passage is structured to lead to which one of the following conclusions?
(A) Houseplants can remove benzene from the air.
(B) Nonsynthetic products do not release toxins into houses.
(C) Keeping houseplants is an effective means of trapping heat in a poorly insulated house.
(D) Keeping houseplants can compensate for some of the negative effects of poor ventilation.（D）
(E) The air in a well-insulated house with houseplants will contain fewer toxins than the air in a well-ventilated house without houseplants.
20. Normal full-term babies are all born with certain instinctive reflexes that disappear by the age of two months. Because this three-month-old baby exhibits these reflexes, this baby is not a normal full-term baby.
Which one of the following has a logical structure most like that of the argument above?
(A) Because carbon dioxide turns limewater milky and this gas is oxygen, it will not turn limewater milky.
(B) Because no ape can talk and Suzy is an ape, Suzy cannot talk.
(C) Because humans are social animals and Henry is sociable, Henry is normal.
(D) Because opossums have abdominal pouches and this animal lacks any such pouch, this animal is not an opossum.（D）
(E) Because some types of trees shed their leaves annually and this tree has not shed its leaves, it is not normal.
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