19. Spectroscopic analysis has revealed the existence of frozen nitrogen, methane¹, and carbon monoxide on the surface of Pluto². Such ices have a tendency to vaporize, producing an atmosphere. Since the proportion of any gas in such an atmosphere depends directly on how readily the corresponding ice vaporizes, astronomers³ have concluded that the components⁴ of Pluto s atmosphere are nitrogen, carbon monoxide, and methane, in order of decreasing abundance.

The astronomers argumetn relies on which one of the following assumptions?

(A) There is no more frozen nitrogen on the surface of Pluto than there is either 　　frozen carbon monoxide or methane.
(B) Until space probes reach Pluto, direct analysis of the atmosphere is 　　impossible.
(C) There is no frozen substance on the surface of Pluto that vaporizes more 　　readily than methane but less readily than carbon monoxide.
(D) Nitrogen is found in the atmosphere of a planet only if nitrogen ice is found 　　on the surface of that planet.
(E) A mixture of nitrogen, carbon monoxide, and methane is characteristic of 　　the substances from which the Solar System formed.

20. Ann will either take a leave of absence from Technocomp and return in a year or else she will quit her job there; but she would not do either one unless she were offerend a one-year teaching fellowship at a prestigious⁵ university. Technocomp will allow her to take a leave of absence if it does not find out that she has been offered the fellowship, but not otherwise, Therefore, Ann will quit her job at Tedhnocomp only if Technocomp finds out she has been oftered the fellowship.

Which one of the following, if assumed, allows the conclusion above to be properly drawn⁶?

(A) Technocomp will find out about Ann being offered the fellowship only if 　　someone informs on her.
(B) The reason Ann wants the fellowship is so she can quit her job at 　　Technocomp.
(C) Technocomp does not allow any of its employees to take a leave of 　　absence in order to work for one of its competitors.
(D) Ann will take a leave of absence if Technocomp allows her to take a leave of 　　absence.
(E) Ann would be offered the fellowship only if she quit her job at Technocomp.

21. If a mechanical aerator⁷ is installed in a fish pool, the water in the pool can be properly aerated⁸. So, since John s fish pool does not have a mechanical aerator, it must be that his pool is not properly aerated. Without properly aerated water, fish cannot thrive. Therefore, any fish in John s fish pool will not thrive.

Which one of the following arguments contains an error of reasoning that is also contained in the argument above?

(A) If alum is added to pickle⁹ brine, brine can replace the water in the pickles¹⁰. 　　Therefore, since Paula does not add alum to her pickle brine, the water in 　　the pickles cannot be replaced by brine. Unless their water is replaced with 　　brine, pickles will not stay crisp. Thus, Paula s pickles will not stay crisp.
(B) If pectin is added to jam, the jam will gel. Without a setting agent such as 　　pectin, jam will not ge. So in order to make his jam gel. Harry¹¹ should add a 　　setting agent such as pectin to the jam.
(C) If stored potatoes are not exposed to ethylene the potatoes will not sprout¹². 　　Beets¹³ do not release ethylene. Therefore, if Sara stores her potatoes 　　together with beets, the potatoes will not sprout.
(D) If a carrot patch is covered with mulch in the fall. the carrots can be left in 　　the ground until spring Without a mulch cover, carrots stored in the ground 　　can suffer frost damage. Thus, since Kevin covers his carrot patch with 　　mulch in the fall, the carrots can safely be left in the ground.
(E) If tomatoes are not stored in a dark place, their seeds sometimes sprout. 　　Sprouted¹⁴ seeds can make tomatoes inedible¹⁵. Therefore, since Maria does 　　not store her tomatoes in a dark place some of Maria s tomatoes could be 　　inedible.

Questions 22-23

　　Antinuclear activist¹⁶: The closing of the nuclear power plant is a victory for the antinuclear cause. It also represents a belated acknowledgment by the power industry that they cannot operate such plants safely.

　　Nuclear power plant manager : It represents no such thing. The availability of cheap power from nonnuclear sources. together with the cost of mandated¹⁷ safety inspections¹⁸ and safety repairs, made continued operation uneconomic. Thus it was not safety considerations but economic considerations taht dictated the plant s closing

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