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根据下面资料，回答题 Among the raft of books, articles, jokes, romantic comedies, self-help guides and otherwritings discussing marriage, some familiar ideas often crop up．Few appear more often than the(21) that many old couples look alike．You have probably seen it before--two elderlypeople walking hand-in-hand down the street or sitting at a cafe, (22) each other sostrongly that they could be siblings．Do these couples actually look alike, and if (23) ,what has caused them to develop this way?
A study published in the March 2006 issue of Personality and Individual Differences may havethe (24) ．Twenty-two people, divided equally between male and female, participated inthe study．They were asked to judge the looks, personalities and ages of 160 married couples．Theparticipants viewed photographs of men and women separately and were (25) told whowas married to whom．The subjects consistently judged people who were married (26) being similar (27) appearance and personality．The researchers also found that couples who had been together longer appeared more similar．
This result (28) itself may'not seem surprising, but the study also offered some answers on (29) couples may look alike．To start, consider that life experiences can end up being reflected physically．Someone (30) is happy and smiles more will develop the facial muscles and wrinkles related to smiling．The years of experience of an elderly couple' s marriage, happy (31) not, would then be reflected in their (32) Genetic influences are (33) factor．A past study showed that genetically similar people have better marriages．Such families have (34) incidents of child abuse and a lower rate of miscarriages．People also appear to be more selfless (35) involved with genetically similar partners．
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