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Read the following text. Choose the best word(s) for each numbered blank and mark A, B, C or D on ANSWER SHEET 1. (10 points)

　Though not biologically related, friends are as “related” as fourth cousins, sharing about 1% of genes. That is 　1　 a study published from the University of California and Yale University in the Proceedings of the National Academy of Sciences, has 　2　.

　The study is a genome-wide analysis conducted 　3　 1932 unique subjects which 　4　 pairs of unrelated friends and unrelated strangers. The same people were used in both 　5　.

　While 1% may seem 　6　, it is not so to a geneticist. As James Fowler, professor of medical genetics at UC San Diego says, “Most people do not even 　7　 their fourth cousins but somehow manage to select as friends the people who 　8　 our kin. ”

　The study 　9　 found that the genes for smell were something shared in friends but not genes for immunity. Why this similarity exists in smell genes is difficult to explain, for now. 　10　, as the team suggests, it draws us to similar environments but there is more 　11　 it. There could be many mechanisms working together that 　12　 us in choosing genetically similar friends 　13　 “functional kinship” of being friends with 　14　!

　One of the remarkable findings of the study was that the similar genes seem to be evolving 　15　 than other genes. Studying this could help 　16　 why human evolution picked pace in the last 30,000 years, with social environment being a major 　17　 factor.

　The findings do not simply explain people’s 　18　 to befriend those of similar 　19　 backgrounds, say the researchers. Though all the subjects were drawn from a population of European extraction, care was taken to 　20　 that all subjects, friends and strangers were taken from the same population. The team also controlled the data to check ancestry of subjects.

15． ______