Experts pls help :strengthen the argument QUERY !

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Toxicologist: A survey of oil-refinery workers who work with MBTE, an ingredient currently used in some smog-reducing gasoline, found an alarming incidence of complaints about headaches, fatigue, and shortness of breath. Since gasoline containing MBTE will soon be widely used, we can expect an increased incidence of headaches, fatigue, and shortness of breath.

Each of the following, if true, strengthens the toxicologist's argument EXCEPT:

(A) Most oil-refinery workers who do not work with MBTE do not have serious health problems involving headaches, fatigue, and shortness of breath.
(B) Headaches, fatigue, and shortness of breath are among the symptoms of several medical conditions that are potentially serious threats to public health.
(C) Since the time when gasoline containing MBTE was first introduced in a few metropolitan areas, those areas reported an increase in the number of complaints about headaches, fatigue, and shortness of breath.
(D) Regions in which only gasoline containing MBTE is used have a much greater incidence of headaches, fatigue, and shortness of breath than do similar regions in which only MBTE-free gasoline is used.
(E) The oil-refinery workers surveyed were carefully selected to be representative of the broader population in their medical histories prior to exposure to MBTE, as well as in other relevant respects.






[spoiler]My Query :
I was stuck up between B & E.Offcourse the OA is B as it does not add anything to the conclusion & hence is NOT the strengthener.
but Experts can u pls tell me where I am wrong here by thinking that since in E, the "oil-refinery workers surveyed were carefully selected to be representative of the broader population in their medical histories prior to exposure to MBTE, as well as in other relevant respects." my thoughts were that they would represent a BIASED sample who already had a previous medical histories prior to exposure & hence this choice wWEAKENS the argument.
The explaination says :(This option strengthen the conclusion as it shows that the sample chosen for survey were representative of the population)

Thanks in advance.
~Himu.[/spoiler]
Source: — Critical Reasoning |

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by Brent@GMATPrepNow » Thu Mar 28, 2013 6:19 am
Having "medical histories prior to exposure" does not imply anything about bias. Everyone has a medical history.
All answer choice E is saying is that the workers survey were representative of the broader population.

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Brent
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by beatthe800 » Sat Mar 30, 2013 9:59 pm
Agree with Himu.. Whats problem with E?

Please explain.

Thanks-
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by Ankur87 » Sun May 05, 2013 5:17 am
Himu is absolutely right.
I also chose B as this choice is out of scope, though wasn't able to eliminate E .

This choice is somewhat confusing, I didn't understand how can it strengthens the toxicologist's argument.