Theproblem________whenthestudentsrefusedtodotheirhomework.

若函数在x=0处连续，则（）

Theaddressbook________theemailaddressesofyourfriendsorgroupsofcolleagues.

设A,B,C为三个随机事件,且P(A)=P(B)=P(C)=1/4,P(AB)=0,P(AC)=P(BC)=1/12,则A,B,C中恰有一个事件发生的概率为()

________(fail)severaltimes,theyneedsomeencouragement.