Tostudyaforeignlanguage,__________.
Theboyranoutoftheclassroomwithouttheteacher's_______.
Wemust______thattheexperimentiscontrolledasrigidlyaspossible.
Thewealthofacountryshouldbemeasured________thehealthandhappinessofitspeopleaswellasthematerialgoodsitcanproduce.