Many older people look back on their lives, and regret that they did not obtain some good vocational guidance [when they were in high school. Is there any way of deciding whether you have chosen a suitable course of study? There is no simple answer to this question. But if you enjoy your work, are interested in it, and are not strongly attracted by other professions and courses of training, you have probably chosen reasonably well. Since in some colleges as many as 40 percent of students change their vocational choice in the course of their studies, vocational guidance would seem to be desirable. In a sample of eminent men, it was found that only one-third had chosen their profession on leaving school.
Ｂ 適切な職業指導（good vocational guidance）がなぜ高校のときに必要と考えられるのか、筆者が述べている具体的な理由を一つあげなさい。（50字以内で書きなさい。ただし、句読点を含みます。）