Critical Reasoning (CR) | Some astrologers claim that personalities are completely determine

Some astrologers claim that personalities are completely determine by horoscopes, but this claim is false. Identical twins born at practically the same time often do have similar personalities. Nevertheless, when birth records were examined to track two individuals - born 40 years ago on the same day and at exactly the same time, one in Toronto and one in New York - their personalities were found to be entirely different.

Which one of the following is an assumption on which the argument depends?
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