A、Friends are more alike brothers and sisters. B、It is simple for friends to start a conversation. C、Friends have some genes in

(16)When we make friends, it can help to have something in common. Researchers and anyone who has ever struck up conversation with a stranger know this. But a new study published in the Proceedings of the National Academy of Sciences finds that commonality among friends goes far deeper:(17)Friends resemble each other genetically. In fact, the genetic similarity was enough to create an explanation from which researchers can predict. Scientists were confident that those in a group of genes will be friends. This confidence was at the same level as they currently have for predicting a person’s chances of obesity or schizophrenia. Friends, it turns out, have about the same amount of genes in common as fourth cousins, or people who have the same great-great-great grandparents, which amounts to about one percent of genes, according to the study.(18)The researchers pulled data from 1 932 individuals—most of whom were of European descent—controlled for already well-established factors like people’s tendency to befriend those of similar ethnic backgrounds. The study compared pairs of unrelated friends against pairs of unrelated strangers. The research showed that we have more DNA in common with the people we pick as friends than we do with strangers in the same population. Fowler and Christakis found that(19)friends are most similar in genes that affect sense of smell, which comes with no obvious explanation. They hypothesize that people with similar smell genes might encounter each other in similar smelling environments and then become friends. But they suspect that "there is more to the story than that."
16. What may help in making friends between strangers?
17. What does the new study find?
18. What can we learn about the study?
19. What genes are most similar among friends?