按其内容和功用的不同，可将常用的通知分为以下几种：（1）（）性通知；（2）（）性通知；（3）（）性通知；（4）（）性通知。
参考答案：批示；指示；告知；任免
About ______ of these books ______ sold out. [ ]
A. two thirds; have
B. two thirds; has
C. two third; have been
D. two third; has been
软岩称为不稳定岩石，其强度定义为：单向抗压强度小于（）的岩石。
A.15MPa
B.25MPa
C.35MPa
