Staying positive through the cold season could be your best defense against getting ill, new study findings suggest. In an experiment that exposed healthy volunteers to a cold or flu virus, researchers found that people with a generally sunny character were less likely to fall ill. The findings, published in the journal Psychosomatic Medicine, build on evidence that a "positive emotional style" can help to protect us from suffering the common cold and other illnesses. Researchers believe the reasons may be both objective -- as in happiness improving immune function -- and subjective -- as in happy people being less troubled by a sore throat or runny nose. "People with a positive emotional style may have different immune responses to the virus," explained lead study author Dr Sheldon Cohen of Carnegie Mellon University in Pittsburgh. "And when they do get a cold, they may interpret their illness as being less severe." Cohen and his colleagues had found in a previous study that happier people seemed less likely to catch a cold, but some questions remained as to whether the emotional style itself had the effect. For the new study, the researchers had 193 healthy adults complete standard measures of personality characteristics, self-felt health and emotional style. Those who had a tendency to be happy, energetic and easy-going were judged as having a positive emotional style, while those who were often unhappy, tense and aggressive had a negative style. The researchers gave them nasal   drops containing either a cold virus or a particular flu virus. Over the next six days, the volunteers reported on any aches, pains or sneezing they had, while the researchers collected objective data. Cohen and his colleagues found that based on objective measures of nasal troubles, happy people were less likely to develop a cold. According to Dr Cohen's research, the reason why some people are unlikely to catch a cold may be that   _  .
their cheerful mood benefits the immune system they have developed a certain way against flu virus they are less likely to have a sore throat and runny nose they have got a stronger self-confidence in their health
Question: Staying positive through the cold season could be your best defense against getting ill, new study findings suggest. In an experiment that exposed healthy volunteers to a cold or flu virus, researchers found that people with a generally sunny character were less likely to fall ill. The findings, published in the journal Psychosomatic Medicine, build on evidence that a "positive emotional style" can help to protect us from suffering the common cold and other illnesses. Researchers believe the reasons may be both objective -- as in happiness improving immune function -- and subjective -- as in happy people being less troubled by a sore throat or runny nose. "People with a positive emotional style may have different immune responses to the virus," explained lead study author Dr Sheldon Cohen of Carnegie Mellon University in Pittsburgh. "And when they do get a cold, they may interpret their illness as being less severe." Cohen and his colleagues had found in a previous study that happier people seemed less likely to catch a cold, but some questions remained as to whether the emotional style itself had the effect. For the new study, the researchers had 193 healthy adults complete standard measures of personality characteristics, self-felt health and emotional style. Those who had a tendency to be happy, energetic and easy-going were judged as having a positive emotional style, while those who were often unhappy, tense and aggressive had a negative style. The researchers gave them nasal   drops containing either a cold virus or a particular flu virus. Over the next six days, the volunteers reported on any aches, pains or sneezing they had, while the researchers collected objective data. Cohen and his colleagues found that based on objective measures of nasal troubles, happy people were less likely to develop a cold. According to Dr Cohen's research, the reason why some people are unlikely to catch a cold may be that   _  .
A. their cheerful mood benefits the immune system
B. they have developed a certain way against flu virus
C. they are less likely to have a sore throat and runny nose
D. they have got a stronger self-confidence in their health
Answer: