单选题 A joint probability of A and B must always be: A. less than or equal to the conditional probability of A given B. B. greater than or equal to the conditional probability of A given B. C. greater than or equal to than the probability of A or B.

【正确答案】 A

【答案解析】By the formula for joint probability: P(AB)=P(A|B)×P(B), since P(B)≤1, then P(AB)≤P(A|B). None of the other choices must hold.