Could a hug a day keep the doctor away?The answer may be a resounding"yes!"___1__helping you feel close and__2___to people you care about,it turns out that hugs can bring a___3__of health benefits to your body and minD.Believe it or not,a warm embrace might even help you__4___getting sick this winter.In a recent study___5__over 400 healthy adults,researchers from Carnegie Mellon University in Pennsylvania examined the effects of perceived social support and the receipt of hugs___6__the participants'susceptibility（敏感性）to developing the common cold after being___7__to the virus.People who perceived greater social support were less likely to come___8__with a cold,and the researchers__9___that the stress-reducing effects of hugging___10__about 32 percent of that beneficial effect.___11__among those who got a cold,the ones who felt greater social support and received more frequent hugs had less severe__12___."Hugging protects people who are under stress from the___13__risk for colds that's usually__14___with stress,"notes Sheldon Cohen,a professor of psychology at Carnegie.Hugging"is a marker of intimacy and helps__15___the feeling that others are there to help___16__difficulty."Some experts___17__the stress-reducing,health-related benefits of hugging to the release of oxytocin（后叶催产素）,often called"the bonding hormone"__18___it promotes attachment in relationships,including that between mothers and their newborn babies.Oxytocin is made primarily in the central lower part of the brain,and some of it is released into the bloodstream.But some of it___19__in the brain,where it__20___mood,behavior and physiology.18选？

• A.unless
• B.because
• C.though
• D.until