Critical Reasoning

jainrahul1985 wrote:In 1986, the city of Los Diablos had 20 days on which air pollution reached unhealthful amounts and a smog alert was put into effect. In early 1987, new air pollution control measures were enacted, but the city had smog alerts on 31 days that year and on 39 days the following year. In 1989, however, the number of smog alerts in Los Diablos dropped to sixteen. The main air pollutants in Los Diablos are ozone and carbon monoxide, and since 1986 the levels of both have been monitored by gas spectrography.
Which of the following statements, assuming that each is true, would be LEAST helpful in explaining the air pollution levels in Los Diablos between 1986 and 1989?
(A) The 1987 air pollution control measures enacted in Los Diablos were put into effect in November of 1988.
(B) In December of 1988 a new and far more accurate gas spectrometer was invented.
(C) In February of 1989, the Pollution Control Board of Los Diablos revised the scale used to determine the amount of air pollution considered unhealthful.
(D) In 1988 the mayor of Los Diablos was found to have accepted large campaign donations from local industries and to have exempted those same industries from air pollution control measures.
(E) Excess ozone and carbon monoxide require a minimum of two years to break down naturally in the atmosphere above a given area.

Confused b/w B , C and D . Experts please suggest

jainrahul1985 wrote:In 1986, the city of Los Diablos had 20 days on which air pollution reached unhealthful amounts and a smog alert was put into effect. In early 1987, new air pollution control measures were enacted, but the city had smog alerts on 31 days that year and on 39 days the following year. In 1989, however, the number of smog alerts in Los Diablos dropped to sixteen. The main air pollutants in Los Diablos are ozone and carbon monoxide, and since 1986 the levels of both have been monitored by gas spectrography.

Which of the following statements, assuming that each is true, would be LEAST helpful in explaining the air pollution levels in Los Diablos between 1986 and 1989?

We need to find a choice that is LEAST helpful in explaining the sudden decrease in 1989.

(A) The 1987 air pollution control measures enacted in Los Diablos were put into effect in November of 1988. --> So the control measures probably came into effect later and helped. Better late than never! Helpful

(B) In December of 1988 a new and far more accurate gas spectrometer was invented. --> An accurate gas spectrometer helped give better results. What if the pollution level WERE already down but was never perceptible because of the lack of a good spectrometer? Helpful.

(C) In February of 1989, the Pollution Control Board of Los Diablos revised the scale used to determine the amount of air pollution considered unhealthful. --> Revised. Was the scale decreased or increased? If decreased, the result should not have gone down. Instead it should have gone up. So was probably increased. That helps in explaining the decrease in levels too. Helpful (but doubtful about my logic in refuting)

(D) In 1988 the mayor of Los Diablos was found to have accepted large campaign donations from local industries and to have exempted those same industries from air pollution control measures. --> Well, the industries were exempted from pollution control measures but in all probability their pollution levels remained the same. So this, IMO, does not help explain why the levels decreased in 1989. Besides on second thoughts, that industries were the reason behind high pollution levels is not mentioned in the premise. So this ideally should be the least helpful.

(E) Excess ozone and carbon monoxide require a minimum of two years to break down naturally in the atmosphere above a given area. --> Minimum of two years suggests that 1989 is when the level should go down. Helpful.

Confused b/w B , C and D . Experts please suggest

jainrahul1985 wrote:In 1986, the city of Los Diablos had 20 days on which air pollution reached unhealthful amounts and a smog alert was put into effect. In early 1987, new air pollution control measures were enacted, but the city had smog alerts on 31 days that year and on 39 days the following year. In 1989, however, the number of smog alerts in Los Diablos dropped to sixteen. The main air pollutants in Los Diablos are ozone and carbon monoxide, and since 1986 the levels of both have been monitored by gas spectrography.
Which of the following statements, assuming that each is true, would be LEAST helpful in explaining the air pollution levels in Los Diablos between 1986 and 1989?
(A) The 1987 air pollution control measures enacted in Los Diablos were put into effect in November of 1988.
(B) In December of 1988 a new and far more accurate gas spectrometer was invented.
(C) In February of 1989, the Pollution Control Board of Los Diablos revised the scale used to determine the amount of air pollution considered unhealthful.
(D) In 1988 the mayor of Los Diablos was found to have accepted large campaign donations from local industries and to have exempted those same industries from air pollution control measures.
(E) Excess ozone and carbon monoxide require a minimum of two years to break down naturally in the atmosphere above a given area.

Confused b/w B , C and D . Experts please suggest

lunarpower wrote:i received a private message about this thread.

as in the case of similar problems, you must figure out what you're trying to explain before you pick out explanations for it.
in this problem, the following data are given:
* the new smog laws went into effect in early 1987
* the number of smog alerts actually went up in 1987-88
* the number of smog alerts then dropped sharply in 1989

remember, you're not trying to prove anything in these problems; you're just trying to pick out those explanations that could reasonably account for the observed effects.

a) this statement would give a nice explanation for the two-year delay between the enactment of the laws and the drop in smog alerts.
b) the introduction of a more accurate measuring instrument could theoretically explain any abrupt change in measurements, regardless of whether that change might be an increase or decrease. therefore, the introduction of this new spectrometer could account for the abrupt changes in 1989.
c) since the problem gives data in terms of smog alerts, rather than in terms of the quantitative amount of smog in the atmosphere, a change in the smog-alert threshold level will have an obvious effect on the data. as in choice (b), the word "revised" doesn't specifically imply that the threshold was made more lax -- the change could have gone either way -- but the point is that a change in this threshold can reasonably account for the observed changes.
d) there is no direct connection between these behaviors and the observed quantities of smog alerts. moreover, if the mayor exempted the industries from air pollution control in 1988, then this consideration actually runs counter to the observed data, because the number of smog alerts actually went down after the mayor removed these industries from control.
e) this statement would give a nice explanation for the two-year delay between the enactment of the laws and the drop in smog alerts.