Itisusefultoscience_______theearthasanobjectinspace.
Whenworkersareorganizedintradeunions,employersfindithardtolaythem________.
Humanbehaviorismostlyaproductoflearning________thebehaviorofanimalsdependsmainlyoninstinct.
EachyearintheUnitedStates,manyblackteenagers_______ofschool,eitherbecausetheycannotkeepuportheyhavetoworktosupporttheirfamily.
WhenIcamethroughthecustomsattheairport,Ihadtopay________onaclockIhadbought.