Whenhesuddenly________upthesubjectofgeneticengineering,therewasanembarrassedsilence.
Thewealthofacountryshouldbemeasured________thehealthandhappinessofitspeopleaswellasthematerialgoodsitcanproduce.
Whenworkersareorganizedintradeunions,employersfindithardtolaythem________.
WhenIcamethroughthecustomsattheairport,Ihadtopay________onaclockIhadbought.