题目内容：
根据材料，完成题。The Choice of an Occupation Most worthwhile careers require some kind of specialized training. Ideally, therefore, the choice of an occupation should be made even before the choice of a curriculum in high school. Actually, 51, most people make several job choices during their working lives,52because of economic and industrial changes and partly to improve53position. The "one perfect job" does not exist. Young people should54enter into a broad flexible training program that will fit them for a field of work rather than for a single55
Unfortunately many young people have to make career plans without benefit of help from a competent vocational counselor or psychologist. Knowing.56about the occupational world, or themselves for that matter, they choose their lifework on a hit-or-miss basis. Some drift from job to job. Others57to work in which they are unhappy and for which they are not fitted.
One common mistake is choosing an occupation for58real or imagined prestige. Too many high-school students or their parents for them choose the professional field, 59both the relatively small proportion of workers in the professions and the extremely high educational and personal60The imagined or real prestige of a profession or a "white-collar" job is no good reason for choosing it as life's work.61, these occupations are not always well paid. Since a large proportion of jobs are in mechanical and manual work, the62of young people should give serious63to these fields.
Before making an occupational choice, a person should have a general idea of what he wants64life and how hard he is willing to work to get it. Some people desire social prestige, others intellectual satisfaction.Some want security; others are willing to take65 for financial gain. Each occupational choice has its demands as well as its rewards.
请在第__(51)__处填上正确答案。 A．however
B．therefore
C．though
D．thereby
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