Hello. It’s one of the first words we learn as babies, yet it’s one of the last ones we think to use as adults. That’s unfortunate, b  48  saying hello is more than just saying hello—it is recognition of another’s worth. How might the world change—how might we change—if we mastered this word? To find o 49 , I spent one month saying hello to every person I met. Here’s what I’ve learned.    It can boost （促进） productivity. In one of the few studies ever done on this subject, Allan Allday, a 50  assistant professor of special education at Oklahoma State University, had middle school teachers greet their students individually each morning. This exchange of greetings raised the kids’ productivity. School went from impersonal to p 51 , and that resulted in more class participation and better grades.
Environments influence friendliness, One study found that people in the city were more likely to kiss one hand with a stranger than those in the countryside. And researchers say，pleasure environments generally encourage more smiles and hellos t 52  unpleasant ones. My experience was similarly. Whatever the reason, my urban hellos were answered far l 53  often than my rural one. Similarly, people in vacation spots, l 54  the Jersey Shore, were far friendlier than those hurrying work downtown. 
It’s a form of universal health insurance. It’s impossible to say hello w 55  smiling. And smiling has been shown to lower blood pressure, relieve stress and boost happiness. Apparently, a smile creates a similar effect in the recipient （接受者）。