未知题型 由联合密度函数可以求解边缘密度函数，但是边缘密度函数不一定能得到联合密度函数

单项选择题 根据以下材料，回答题Sometimes I really doubt whether there islove between my parents. They are very busy working to 16 the family. They don′t act in the 17 ways that I read in books or I see on TV.18 flowers to

单项选择题 But not all pretended deeds have to fallshort of their normal function in order to ______ their communication purpose.