You are misunderstanding the reasoning behind the argument and correct answer choice.
We are told that a good clue as to which geographical regions an ancient relic was moved through in the past involves the analysis of pollen that clings to the surface of the relic. They identify the pollen from plants that are known to have been unique to that area and link the relic to those geographical areas.
We are looking for the answer choice that weakens the reliability of the method described.
Answer choice (A) states: "Pollens are often transported from one region to another by wind or human movement."
This weakens the reliability of the method because the pollen of a far off area, e.g. area A, could have been carried by the wind to land on the relic as it was traveling through a nearby area, e.g. area B--thereby causing researchers to believe that the relic traveled through area A as well because pollen from area A was found on it, when in reality the wind merely carried the pollen from area A to the relic.
Thus, answer choice (A) brings the reliability of the method described above, merely looking at the region where the pollen is from to attribute to where the relic traveled through, in doubt.
Hope that clears things up! Please let us know if you have any other questions.