18. Prolonged exposure to nonionizing radiation—electromagnetic radiation at or below the frequency of visible light—increases a person s chances of developing soft-tissue cancer. Electric power lines as well as such electrical appliances as electric blankets and video-display terminals are sources of nonionizing radiation.

　　Which one of the following conclusions is best supported by the statements above?

(A) People with short-term exposure to nonionizing radiation are not at risk of 　　developing soft-tissue cancers.
(B) Soft-tissue cancers are more common than other cancers.
(C) Soft-tissue cancers are frequently cured spontaneously when sources of 　　nonionizing radiation are removed from the patient s home.
(D) Certain electrical devices can pose health risks for their users.
(E) Devices producing electromagnetic radiation at frequencies higher than that 　　of visible light do not increase a person s risk of developing soft-tissue 　　cancers.

19. In the first decade following the founding of the British Labour party, the number of people regularly voting for Labour increased fivefold. The number of committed Labour voters increased a further fivefold during the party s second decade. Since the increase was thus the same in the first as in the second decade, the often-made claim that the Labour party gained move voters in the party s second decade than in its first is clearly false.

　　The reasoning in the argument is flawed because the argument

(A) fails to specify¹ dates necessary to evaluate the truth of the conclusion, even 　　though the argument depends on distinguishing between two time periods
(B) draws a conclusion that cannot be true if all the data advanced in its support 　　are true
(C) relies on statistical² evidence that, strictly³ speaking, is irrelevant⁴ to 　　establishing the conclusion drawn
(D) fails to allow for the possibility that the policy positions advocated by the 　　Labour party changed during the period in question
(E) overlooks the possibility that more elections were held in one of the two 　　decades than were held in the other

Questions 20-21

　　A number of seriously interested amateur astronomers⁵ have tested the new Exodus⁶ refractor telescope. With it, they were able to observe in crisp detail planetary features that were seen only as fuzzy images in their 8-inch (approximately 20-centimeter) Newtonian telescopes, even though the 8-inch telescopes, with their wider apertures⁷, gather more light than the 4-inch (approximately 10-centimeter) Exodus. Given these amateur astronomers observational findings, any serious amateur astronomers ought to choose the Exodus if she or he is buying a telescope for planetary observation.

20. The argument proceeds by

(A) evaluating the credibility of claims made by a particular group
(B) detailing the ways in which a testing situation approximates the conditions 　　of ordinary use
(C) placing a phenomenon in a wider context in order to explain it
(D) supporting a recommendation to a group on the basis of the experience of a 　　subset of that group
(E) distinguishing between the actual reasons why a certain group did a 　　particular thing and the best reasons for doing that thing.

21. Which one of the following most seriously weakens the argument?

(A) Telescopes of certain types will not perform well unless they have been 　　precisely⁸ collimated a delicate adjustement requriring deftness⁹.
(B) Image quality is only one of several different factors that, taken together, 　　should determine the choice of a telescope for planetary observation.
(C) Many serious amateur astronomers have no intention of buying a telescope 　　for planetary observation.
(D) The comparisons made by the amateur astronomers were based on 　　observations made during several different observation sessions.
(E) The substance used to make the lenses of Exodus telescopes differs from 　　that used in the lenses of other telescopes

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