4．The faces of the elderly，happily-married people sometimes look like each other．Dr．Aiken studied a number of couples who had been married for at least twenty-five years．Each couple provided four photographs-one photo of each partner at the time of their marriage and another photo to remove any clues．The photos were then displayed in groups：a random（隨意的）grouping of the persons at the time of their marriage and another random grouping of the same persons who took photographs later．Some judges were asked to pick out the partners．They failed totally with the first group．Their judgments were no better than chance．But with the photos taken twenty-five or more years after the marriage，the judges were quite successful at deciding who was married to whom．They were particularly successful with the most happily-married couples．
Dr．Aiken believes there are several reasons why couples grow alike．One reason has something to do with imitation．One person tends to copy or do the same as someone else without knowing it．He says human beings copy the expressions of the faces of their loved ones．Another possible reason，he says，is the common experience of the couples．There is a tendency for people who have the same life experience to change their faces in similar ways．For example，if a couple suffered a lot of sad experiences，their faces are likely to change in a similar way．
21．The main purpose of the passage is toC．
A．tell how couples look like each other
B．show the life experience of husband and wife
C．explain why couples grow alike
D．describe the study on a number of married people
22．The judges failed toA．
A．tell couples by looking at their photos taken when they got married
B．tell happily-married couples from sadly-married couples
C．discover the difference of each partner
D．understand Dr．Aiken's study
23．The underlined sentence"Their judgments were no better than chance．"meansC．
A．quite successful
B．based on facts
C．only by luck
D．totally wrong
24．From the passage we can draw a conclusion that．C
A．happily-married couples are often richer than other couples
B．couples who look alike can live longer
C．the influence between couples can be quite strong
D．all couples have been proved to grow alike．
