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

C for me

I go for B
A new accurate gas spectrometer does not explain the decrease

I would go for B.
In December of 1988 a new and far more accurate gas spectrometer was invented. . This means the spectrometer used to test was quite accurate. So this will not explain the huge decrease in the number of alerts.

Hmmm... B, C, D, E .. all choices are already selected.. pretty interesting.
Whats the OA?

- that is not neccessary, it can be the other way round too!

hmmm..i am confused....

Hi vc019,
See the explanation in the link below and you will be convinced that it is B.

http://www.gmatclub.com/phpbb/viewtopic.php?t=32988

Hello vineetgupta,

I agree to the explaination on this link but really it also means that the option B is out of scope of this agrument. I would correct my explaination of point B and say it is out of scope and still say the answer is D.

The reason I would go with D and not with B now is -

B - Out of scope. Invention of a more accurate gas spectrometer does not fall in the scope of the argument.
One of the lessons I would take from this argument is "we should not make our own assumptions" - assuming here that the new spectrometer would be used is an assumption.

So, B does not weaken or strengthen the argument. Hence D is still the answer.

I would really like to know if this explaination is acceptable so that I can be sure that the line of thought is correct.
Regards

VC