求助-大全-II-13

13.

Of those person who became teachers in 1968 and who later left the profession, 30 percent today earn salaries above $35,000 a year: of those who became teachers in 1968 and have remained in the profession, only 15 percent today earn salaries above $35,000 a year. These figures indicate how underpaid teachers are today.
The argument above depends on which of the following assumptions about the persons for whom statistics are cited?
(A) At least one-third of the group of persons who have remained in teaching would today be earning more than $35,000 a year if they had left teaching.
(B) The group of persons who left teaching and the group who did not are comparable in terms of factors that determine how much people outside the teaching profession are paid.
(C) Most of those persons who left teaching did so entirely because of the low salaries teachers earn.
(D) As a group, those persons who have remained in teaching are abler and more dedicated than the group of persons who left teaching.
(E) The group of persons who left teaching and who today earn more than $35,000 a year were more capable teachers than the group who remained in the profession.

答案為什麼是B呢?

Try deny test.  Deny B, we get "Those people who left teaching and those did not are not comparable in factors that determine their earning power outside the teaching profession."  In other words, these two groups' pay are unequal because they have inherently different earning power factors.  If so, the argument's conclusion that "teachers are underpaid today" will fall apart.  Therefore, B is a necessary assumption, and the best answer.