第23题: [单项选择]The last half of the nineteenth century ______ the steady improvement in the means of travel. A. has witnessed B. was witnessed C. witnessed D. is witnessed 参考答案:C 答案解析:[注释] 根据主语可判断出时间为过去时。
第27题:[单选题]设
A、B为两个事件,P
(B) >0,且A包含于
B,则( )一定成立。
A. P(A
B) ≤1 A.P(B B. C.P(A D.=0 参考答案:A 因为A包含于B,即P(AB) =P(A),且P(A)≤P(B),所以P(A B) =P(AB)/P(B)=P(A)/P(B)≤1。