Dr. Jack M. Gwaltney, Jr. a professor at the University Of Virginia School Of Medicine infected six student volunteers with virus, the most common cause of colds. A few days later, when they were coughing and sneezing, he gathered 37 more people and divided them into three groups. Group 1 members spent three days and nights in the same room with one of the infected students, separated by a screen so they couldn't touch one another. Group 2 sat around a table while an infected volunteer talked, coughed and sang to them. Group 3 held hands with an infected student for ten seconds, and then touched their own noses or eyes. Although most scientists at the time, the mid-70s, believed colds were spread by virus-laden droplets spread through the air when infected people coughed or sneezed, Gwaltney suspected physical contact might play an important role. Sure enough, of the 15 people who had touched a student volunteer, 11 became infected--compared with only one of those who had been sitting at the table, and none who had spent three days and nights together. "The best evidence we have is that hand-to-hand contact is the most efficient way of transmitting virus," says Gwaltney. The study was one of a series that helped establish Gwaltney's reputation as a leading authority. Dr. Robert Couch says, "It would not be inappropriate to call him Mr. Common Cold." When Gwaltney is asked how close scientists are to finding a cure, he replies: "If you mean 'get rid of', I don't think we're going to be able to do that with cold viruses any time soon. But if you look in the dictionary, you'll see that 'cure' is explained as a successful treatment. And we're not just getting more effective at treating the symptoms  --we're getting at the root cause too. " The result of the experiment shows that   _   plays an important role in the infection of colds.
sneezing at the infected person touching the infected person sitting together with the infected person talking with the infected person
Question: Dr. Jack M. Gwaltney, Jr. a professor at the University Of Virginia School Of Medicine infected six student volunteers with virus, the most common cause of colds. A few days later, when they were coughing and sneezing, he gathered 37 more people and divided them into three groups. Group 1 members spent three days and nights in the same room with one of the infected students, separated by a screen so they couldn't touch one another. Group 2 sat around a table while an infected volunteer talked, coughed and sang to them. Group 3 held hands with an infected student for ten seconds, and then touched their own noses or eyes. Although most scientists at the time, the mid-70s, believed colds were spread by virus-laden droplets spread through the air when infected people coughed or sneezed, Gwaltney suspected physical contact might play an important role. Sure enough, of the 15 people who had touched a student volunteer, 11 became infected--compared with only one of those who had been sitting at the table, and none who had spent three days and nights together. "The best evidence we have is that hand-to-hand contact is the most efficient way of transmitting virus," says Gwaltney. The study was one of a series that helped establish Gwaltney's reputation as a leading authority. Dr. Robert Couch says, "It would not be inappropriate to call him Mr. Common Cold." When Gwaltney is asked how close scientists are to finding a cure, he replies: "If you mean 'get rid of', I don't think we're going to be able to do that with cold viruses any time soon. But if you look in the dictionary, you'll see that 'cure' is explained as a successful treatment. And we're not just getting more effective at treating the symptoms  --we're getting at the root cause too. " The result of the experiment shows that   _   plays an important role in the infection of colds.
A. sneezing at the infected person
B. touching the infected person
C. sitting together with the infected person
D. talking with the infected person
Answer: