Psychologist: Some astrologers claim that our horoscopes completely determine our personalities, but this claim is false. I concede that identical twins -- who are, of course, born at practically the same time -- often do have similar personalities. However, birth records were examined to find two individuals who were born 40 years ago on the same day and at exactly the same time -- one in a hospital in Toronto and one in a hospital in New York. Personality tests revealed that the personalities of these two individuals are in fact different. Which one of the following is an assumption on which the psychologist's argument depends? ['The personality differences between the two individuals cannot be explained by the cultural differences between Toronto and New York.', 'Astrologers have not subjected their claims to rigorous experimentation.', 'Complete birth records for the past 40 years were kept at both hospitals.', 'The geographical difference between Toronto and New York did not result in the two individuals having different horoscopes.']