It'smore________tobuyaseasonticketifyoutraveleveryday.
Wemust______thattheexperimentiscontrolledasrigidlyaspossible.
Whenhesuddenly________upthesubjectofgeneticengineering,therewasanembarrassedsilence.
Thestudentfoundthenovel_______.Itprovidedhimwithsomuchinformationaboutthesubject.
SinceWilliamhadbeenseriouslyillforseveralmonths,hisparentswereworriedabout________toreturntoschoolfull-time.
WhenIcamethroughthecustomsattheairport,Ihadtopay________onaclockIhadbought.