Mr. Brown is 102 years old. He is leading a full and active life. Why has he【21】so long? Many【22】would like to know the answer to the question. They are studying groups of old people all over the world and try to find why some very old people remain healthy【23】and spirit (精神) while【24】be come weak and iii in their 60s. They have observed, first of all, that doing【25】work is a way of life for all these long-lived people. They began their long days of physical labor【26】children and never seem to stop. Second, all these people come from【27】. The air has【28】oxygen (氧) and is pollution free,【29】makes the hearts stronger. Third, these people eat little animal meat. They like to have fresh vegetables, nuts (坚果) , grains, and【30】They never eat more food than their bodies need. (46)