This question is a classic weaken question. There are multiples ways to undermine an argument among which we can mention *unrepresentative sample or any errors that may appear in data which support the conclusion *.
Premise : investigators went into the street and found twenty volunteers born under the sign of Gemini who were willing to be interviewed on the program and to take a personality test.
Premise : The test confirmed the investigators' personal impressions that each of the volunteers was more sociable and extroverted than people are on average
The conclusion is : one's astrological birth sign influence one's personality. The preceding words clearly show that all that was mentioned in the text is mentioned to claim the final sentence of the stimulus which is therefore the conclusion.
Answer A: one may think that if it’s not investigators who administered the test the data are flawed but thinking that way would be helping the argument which clearly did not state that. No information related to the ability of those who conducted the experiment is provided so we cannot conclude anything about the quality of data. So it neither undermines nor helps the argument. Out!
Answer B : actually this one strengthens the argument. Let’s say this another way: Gemini people are more sociable than any other astronomical signs. We can conclude that the astronomical sign plays one role in some sort on the behavior of people. Ouch! Out!
Answer C : This one is irrelevant because the point of the argument is not the impression investigators have on people but the relation between astrological signs of people and their behavior. Ouch! Out!
Answer D : Still irrelevant friendo. Why? Because the argument talks about the relationship between people behavior and their astronomical signs and not between astrological signs and the proportions in the population.
Answer E: If you made till here you are goat because you are right. This answer simply states that the sample is biased in some sort or unrepresentative of the population. Among Gemini only those who are extroverted and sociable participate. There may be some others Gemini who are not sociable and extroverted but we may never know because they do not participate to the experiment.
Mr nobody
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