Over sixty years ago, Dr. Hans Selye recognized the mind-body connection involved with stress, as all of his patients had similar physiological and psychological characteristics. Studies done with laboratory rats found that these same physical responses existed with animals when they were put under stress. He came to the conclusion that stress is "the non-specific response of the body to any demand placed upon it". He concluded that each demand made on the body is unique in that there is a definite response: when we are cold, we shiver; when we are hot we perspire; a great muscular effort increases the demands upon the heart and vascular system.
Selye claimed that it was not stress that harmed us, but distress, and distress occurred when we prolonged emotional stress and didn't deal with it in a positive manner. Selye was the pioneer in research into stress in the 1930s, and is internationally acknowledged as "the father of the stress field'. After publishing the first scientific paper to identify and define "stress" in 1936, Selye wrote more than 1700 scholarly papers and 39 books on the subject. At the time of his death 1982, his work had been cited in more than 362,000 scientific papers, in countless popular magazine stories, and in most major languages. Selye held three earned doctorates (M. D. , Ph. D. , D. Sc. ) plus 43 honorary doctorates, tie was an elected member of several dozen of the world's most recognized medical and scientific associations.
After completion of his academic and professional studies in Prague, Paris, and Rome, Selye received a Rockefeller Research Fellowship and accepted a position at Johns Hopkins University in Baltimore, Maryland. By 1945 he had become the first Director of tile Institute of Experimental Medicine and Surgery at the University of Montreal, Canada. He served in that position until his retirement in 1976. Subsequently he established the International Institute of Stress. He recognized that strain, or stress, plays a very significant nile in the development of all types of disease. Selye called the process whereby strain influences the body, the General Adaptation Syndrome. He concluded that there are three distinctive phases in this process: alarm, resistance, and exhaustion. He wrote of two types of stress: pleasant stress contributing to human well-being, and unpleasant stress contributing to disease. He is still by far the world's most frequently cited author on stress topics.
What does the passage mainly discuss？

A. Selye's professional life and achievements.
B. The origins of the word "stress".
C. Defining stress.
D. The father of the stress field.