[问题] [求助] Pls pls help! SOS!

fernandochang

Pls pls help! I just don't understand the reasoning line? Could you explain me the reasons?

GMAT CRITICAL REASONING OLD QUESTIONS REVIEW
17.State X’s income-averaging law allows a portion of one’s income to be taxed at a lower rate than the rate based on one’s total taxable income. TO use income averaging, the taxpayer must have earned taxable income for a particular year that exceeds 140% of his or her average taxable income for the previous 3 years. People using income averaging owe less tax for that year than they would without income averaging.

Which of the following individuals would be most seriously affected if income averaging were not permitted in computing the taxes owed for the current year?

(A)Individuals whose income has steadily decreased for the past 3 years.
(B)Individuals whose income increased by 50% 4 years ago and has remained the same since then.
(C)Individuals whose income has doubled this year after remaining about the same for 5 years.
(D)Individuals who had no income this year, but did in each of the previous 3 years.
(E)Individuals who are retired and whose income has remained about the same for the past 10 years.
A): C WHY NOT C? [F.26, Q.8]

18.According to a recent study, 15 corporations in the US that follow a credo of social responsibility are also very profitable. Because of their credos, these 15 corporations give generously to charity, follow stringent environmental-protection policies, and have vigorous affirmative-action programs.

Which of the following can be correctly inferred from the statement above?
(A)Following a credo of social responsibility helps to make a corporation very profitable.
(B)It is possible for a corporation that follows a credo of social responsibility to be very profitable.
(C)A corporation that gives generously to charity must be doing so because of its credo of social responsibility.
(D)Corporations that are very profitable tend to give generously to charity.
(E)Corporation that have vigorous affirmative-action programs also tend to follow stringent environmental-protection policies.
A): B [F.26, Q.9]

19.In 1985 the city’s Fine Arts Museum sold 30,000 single-entry tickets. In 1986 the city’s Folk Arts and Interior Design museums opened, and these 3 museums together sold over 30,000 such tickets that year. These museums were worth the cost, since more than twice as many citizens are now enjoying the arts.

Which of the following, if true, most seriously weakens the author’s assertion that more than twice as many citizens are now enjoying the arts?

(A)Most visitors to 1 museum also visit the other 2.
(B)The cost of building the museum won’t be covered by revenues generated by the sale of museum tickets.
(C)As the 2 new museums become better known, even more citizens will visit them.
(D)The city’s Fine Art Museum did not experience a decrease in single-entry tickets sold in 1986.
(E)Fewer museum entry tickets were sold in 1986 than the museum planners had hoped to sell.
A): A WHY NOT E? [F.32, Q.5]

20.Which of the following best completes the passage below?
The unemployment rate in the US fell from 7.5% in 1981 to 6.9% in 1986. It cannot, however, be properly concluded from these statistics that the number of unemployed in 1986 was lower than it had been in 1981 because ___________.

(A)help-wanted advertisements increased between 1981 & 1986.
(B)many of the high-paying industrial jobs available in 1981 were replaced by low-wage service jobs in 1986, resulting in displacements of hundreds of thousands of workers.
(C)in some midwestern industrial states, the unemployment rate was much higher in 1986 than it had been in 1981.
(D)the total available work force, including those with and without employment, increased between 1981 & 1986.
(E)the average time that employees stay in any one job dropped during the period 1981 to 1986.
A): D [F.32, Q.7]

An annually conducted, nationwide survey shows a continuing marked decline in the use of illegal drugs by high school seniors over the last 3 years.

21.Which of the following, if true, casts most doubt on the relevance of the survey results described above for drawing conclusions about illegal drug use in the teen-age population as a whole?
(A)Because of cuts in funding, no survey of illegal drug use by high school seniors will be conducted next year.
(B)The decline uncovered in the survey has occurred despite the decreasing cost of illegal drugs.
(C)Illegal drug use by teen-agers is highest in those areas of the country where teen-agers are least likely to stay in high school for their senior year.
(D)Survey participants are more likely now than they were 3 years ago to describe as “heroic” people who were addicted to illegal drugs and have been able to quit.
(E)The proportion of high school seniors who say that they strongly disapprove of illegal drug use has declined over the last 3 years.
A): C [F.32, Q.10]

22.Which of the following, if true, would provide most support for concluding from the survey results described above that the sue of illegal drugs by people below the age of 20 is declining.
(A)Changes in the level of drug use by high school seniors are seldom matched by changes in the level of drug use by other people below the age of 20.
(B)In the past, high school seniors were consistently the population group most likely to use illegal drugs and most likely to use them heavily.
(C)The percentage of high school seniors who use illegal drugs is consistently very similar to the percentage of all people below the age of 20.
(D)The decline revealed by the surveys is the result of drug education programs specifically targeted at those below the age of 20.
(E)The number of those surveyed who admit to having sold illegal drugs has declined even faster than has the number who have used drugs.
A): C WHY NOT B? [F.32, Q.11]