scientists know that there are two basic approaches to prolonging life. one approach is the __1__ of the diseases that generally __2__ older people ╟ diseases such as cancer, heart attack and stokes. __3__ is the delay of the process of growing old ╟ the __4__ of the body.
 in recent years scientific researchers have spent much time in the study of the process of aging. they believe __5__, within a few years, they will develop the knowledge and the __6__ to delay the aging process for 10 to 15 years. the __7__ will be that more people will live longer, more healthful lives. at present, scientists believe that __8__ the right diet, exercise, medical __9__, and mental attitude many people can live to be 100 years old.
 gerontologists, people who __10__ studies of the problems of growing old, are investigating __11__ body cells slow down and __12__ die. they feel that delaying this slowing down process would help postpone¹ death. in a number of american universities, scientists are __13__ the activity of cells, the effects of diet and internal body temperature __14__ aging. if their studies are successful, the results should help improve the quality of life for older people in the next few years, __15__ increase the life span of the next generation. 
 
1.
a) elimination  b) deletion
c) demonstration d) conduction