Don't get too close to a tired teen ;you could start losing sleep as well.When one teenage

r starts sleeping less, her friends and others in her social【C1】______soon lose sleep, too, according to new research.

Our social networks can【C2】______our behaviors and moods. Political scientist James Fowler of the University of California has studied these effects and previously found that obesity, smoking, and【C3】______happiness can spread through networks of people【C4】______based on their relationships.

Fowler【C5】______his study of a network of more than 8000 7th-to 12th-grade students and their sleeping and smoking【C6】______. He and colleagues【C7】______a web of connections between each student and his or her friends. In one of these friend webs, a gang of sleepless boys【C8】______the middle of the mess, where the most【C9】______kids landed--the so-called "cool" kids. The researchers found that the【C10】______central a teen landed on the map, the greater chance that he or she got less than 7 hours of sleep per night.

Drug use was also contagious(具传染性的), the team【C11】______. Each smoking friend increased the(78 that a student used marijuana(大麻)【C13】______42%. Both sleepless and drug-use contagions could still be felt four-degrees of separation【C14】______, influencing a friend of a friend of a friend's friend.

Most surprisingly, the researchers found a link between【C15】______of sleep and drug use.【C16】______a teen's friend slept less than 7 hours, her chances of using drugs went【C17】______by 19%. And that means that【C18】______sleeplessness spreads throughout a friend【C19】______, drug use spreads as【C20】______.

【C1】

A．bicycle

B．recycle

C．circle

D．cycle