单选题 Which of the following statements is most accurater? A set of events is mutually exclusive means:
A. the events cover all possible outcomes.
B. only one event can occur at a time.
C. the sum of all the events' probabilities equals one.

【正确答案】 B
【答案解析】[解析] 遍历(exhaustive)意味着一组事件包含了所有可能的结果。互斥(mutually exclusive)意味着在同一时间只有一个事件会发生。如果事件之间既是互斥的又是遍历的，那么把所有可能结果的概率累加之和为1。