Wemust______thattheexperimentiscontrolledasrigidlyaspossible.
Idon'tknowhowwecanmake________onthetimetableforanymorecourses.
Whenworkersareorganizedintradeunions,employersfindithardtolaythem________.
________tothepapersisrestrictedtoDefenseDepartmentpersonnelonly.
Insomeschoolschildrenwhoprefertoreadbooksratherthan________footballbecomesocialoutcasts(被抛弃者).