单选题 A government agency publishes ratings of airlines, ranking highest the airlines that have the smallest proportion of late flights. The agency's purpose is to establish an objective measure of the relative efficiency of different airlines' personnel in meeting published flight schedules.
Which one of the following, if true, would tend to invalidate use of the ratings for the agency's purpose?

A、 Travelers sometimes have no choice of airlines for a given trip at a given time.
B、 Flights are often made late by bad weather conditions that affect some airlines more than others.
C、 The flight schedules of all airlines allow extra time for flights that go into or out of very busy airports.
D、 Airline personnel are aware that the government agency is monitoring all airline flights for lateness.
E、 (E) Flights are defined as "late" only if they arrive more than fifteen minutes past their scheduled arrival time, and a record is made of how much later than fifteen minutes they are.

【正确答案】 B

【答案解析】[解析] 上面段落推理为了评价不同航空公司职员的相对有效，可以使用晚点的多少来客观衡量。就目的提方法时，一般用“有他因”来反对。(B)指出“某些班机受天气条件影响要大于其他班机”的其他原因的存在导致晚点，起到了很好的反对作用。(A)、(C)和(D)均为无关选项，(E)给出了晚点的定义，但与“客观公正与否”无关。