农业的社会主义改造中，高级社具有 _________性质。

She got a job as an assistant stage manager at the Cambridge Arts Festival Theatre, thinkingthat it might ________ to a career as a playwright ( 剧作家 ).

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（）

Each year in the United States, many black teenagers _______ of school, either because they cannot keep up or they have to work to support their family.

党在“过渡时期总路线” 中提到的“过渡”是指从 ___________。