EachyearintheUnitedStates,manyblackteenagers_______ofschool,eitherbecausetheycannotkeepuportheyhavetoworktosupporttheirfamily.
________tothepapersisrestrictedtoDefenseDepartmentpersonnelonly.
新民主主义社会是_______。
二维随机变量(X,Y)在D=（x，y）0<y<1-x2上服从均匀分布，求Z1,Z2联合分布。
Night________(fall),wehurriedhome.
