EachyearintheUnitedStates,manyblackteenagers_______ofschool,eitherbecausetheycannotkeepuportheyhavetoworktosupporttheirfamily.
________withthesizeofthewholeearth,thehighestmountainsdonotseemhighatall.
Whenhesuddenly________upthesubjectofgeneticengineering,therewasanembarrassedsilence.
Itisusefultoscience_______theearthasanobjectinspace.
Hethoroughlyunderstoodthesociety__________.
Thewealthofacountryshouldbemeasured________thehealthandhappinessofitspeopleaswellasthematerialgoodsitcanproduce.