单选题 Extraordinarily few people have the ability to be successful commodity traders. So rather than limit the number of people they hire, trading firms aim to hire all those applicants who are able to be successful and to reject the rest. By this standard Quinsey-Leerheim's record is perfect. All of its entry-level hirees over the past decade have become successful commodity traders.
Which of the following, if true, would cast the most doubt on the assessment given above of Quinsey-Leerheim's hiring performance?

A、 Over the past decade, Quinsey-Leerheim's trading practices and policies have changed in a way that gives much more responsibility to individual traders.
B、 Since the pool of entry-level applicants is mostly the same for all commodity-trading firms, Quinsey-Leerheim often competes with other trading firms for the strongest applicants.
C、 Quinsey-Leerheim rejects some entry-level applicants who go on to become extremely successful commodity traders with other trading firms.
D、 Commodity trading requires skills that are needed in very few other occupations, so that trading firms' hiring procedures typically differ significantly from those of other financial firms.
E、 (E) Commodity trading is very stressful, and even successful commodity traders rarely work as traders for longer than ten years, although they often earn substantial sums in those years.

【正确答案】 C

【答案解析】