设A为三阶矩阵,P为可逆矩阵,使得P-1AP=012

I have been studying here for four years, by next summer I ________.

He fell asleep immediately last night; he must ________ (be) very tired.

In the future, more ______ should be placed on the education of the young.

设随机变量 ( Ｘ, Ｙ) 服从二维正态分布，且 Ｘ与Ｙ不相关， f ( x) f ( y) X Y 分别表示 Ｘ，Ｙ的概率密度， 则在Ｙ＝y的条件下， Ｘ的条件概率密度f X|Y （X|Y） 为（）