EachyearintheUnitedStates,manyblackteenagers_______ofschool,eitherbecausetheycannotkeepuportheyhavetoworktosupporttheirfamily.
Thewealthofacountryshouldbemeasured________thehealthandhappinessofitspeopleaswellasthematerialgoodsitcanproduce.
Ishallneverforget________(meet)thelatePremierZhouduringhisinspectionofourfactory.
Theterriblenoiseis______memad.
设二阶可导函数，则（）
