（A） The numbers on the next milepost had been reversed.
（B） The numbers on the mileposts indicate kilometers, not miles.
（C） The facing numbers indicate miles to the end of the path, not miles from the beginning.
（D） A milepost was missing between the two the hiker encountered.
（E） The mileposts had originally been put in place for the use of mountain bikers, not for hikers.
2.Airline: Newly developed collision-avoidance systems, although not fully tested to discover potential malfunctions, must be installed immediately in passenger planes. Their mechanical warnings enable pilots to avoid crashes.Pilots: Pilots will not fly in planes with collision-avoidance systems that are not fully tested. Malfunctioning systems could mislead pilots, causing crashes.The pilots' objection is most strengthened if which of the following is true?
（A） It is always possible for mechanical devices to malfunction.
（B） Jet engines, although not fully tested when first put into use, have achieved exemplary performance and safety records.
（C） Although collision-avoidance systems will enable pilots to avoid some crashes, the likely malfunctions of the not-fully-tested systems will cause even more crashes.
（D） Many airline collisions are caused in part by the exhaustion of overworked pilots.
（E） Collision-avoidance systems, at this stage of development, appear to have worked better in passenger planes than in cargo planes during experimental flights made over a six-month period.
3.Guitar strings often go “dead”—become less responsive and bright in tone—after a few weeks of intense use. A researcher whose son is a classical guitarist hypothesized that dirt and oil, rather than changes in the material properties of the string, were responsible.Which of the following investigations is most likely to yield significant information that would help to evaluate the researcher's hypothesis?
（A） Determining if a metal alloy is used to make the strings used by classical guitarists
（B） Determining whether classical guitarists make their strings go dead faster than do folk guitarists
（C） Determining whether identical lengths of string, of the same gauge, go dead at different rates when strung on various brands of guitars
（D） Determining whether a dead string and a new string produce different qualities of sound
（E） Determining whether smearing various substances on new guitar strings causes them to go dead
4.Most consumers do not get much use out of the sports equipment they purchase. For example, seventeen percent of the adults in the United States own jogging shoes, but only forty-five percent of the owners jog more than once a year, and only seventeen percent jog more than once a week.Which of the following, if true, casts most doubt on the claim that most consumers get little use out of the sports equipment they purchase?
（A） Joggers are most susceptible to sports injuries during the first six months in which they jog.
（B） Joggers often exaggerate the frequency with which they jog in surveys designed to elicit such information.
（C） Many consumers purchase jogging shoes for use in activities other than jogging.
（D） Consumers who take up jogging often purchase an athletic shoe that can be used in other sports.
（E） Joggers who jog more than once a week are often active participants in other sports as well.
5.Two decades after the Emerald River Dam was built, none of the eight fish species native to the Emerald River was still reproducing adequately in the river below the dam. Since the dam reduced the annual range of water temperature in the river below the dam from 50 degrees to 6 degrees, scientists have hypothesized that sharply rising water temperatures must be involved in signaling the native species to begin the reproductive cycle.Which of the following statements, if true, would most strengthen the scientists' hypothesis?
（A） The native fish species were still able to reproduce only in side streams of the river below the dam where the annual temperature range remains approximately 50 degrees.
（B） Before the dam was built, the Emerald River annually overflowed its banks, creating backwaters that were critical breeding areas for the native species of fish.
（C） The lowest recorded temperature of the Emerald River before the dam was built was 34 degrees, whereas the lowest recorded temperature of the river after the dam was built has been 43 degrees.
（D） Nonnative species of fish, introduced into the Emerald River after the dam was built, have begun competing with the declining native fish species for food and space.
（E） Five of the fish species native to the Emerald River are not native to any other river in North America.
