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）__1,932 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 the similar genes seem to be evolution_（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.
5选？
上下文语义衔接+名词辨析根据空格的前后内容判断，到第五个空为止，文章都在讲实验过程，和实验对象，第五个空格所在句子的内容是：相同的人们都用于实验中的这两类______。所以根据上下文语境和内容，应该选与实验对象相对应的samples（样例）。因此，答案是samples。选项A.测试，B.物体，D.事例均不符合前后语境和语义。
