One 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. A relic is linked to a geographical area by the identification of pollen from plants that are known to have been unique to that area. Which one of the following, if true, casts the most doubt on the reliability of the method described above? ['Data are scarce as to the geographical distribution of the pollens of many ancient plants.', 'Pollens are often transported from one region to another by wind or human movement.', 'Many types of pollen were common to several geographical regions in the ancient world.', 'Pollen analysis is a painstaking process that is also expensive to conduct.']