Since William had been seriously ill for several months, his parents were worried about________ to return to school full-time.
D
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Thefarmerhadtowearheavybootsinthewinterbecausethefieldsweretoowetand________.
Seniormembersofthestaffcompetedeagerly________thepositionofsalesmanagerinthecompany.
Wemust______thattheexperimentiscontrolledasrigidlyaspossible.
TheTVstation,in________tomassivepopulardemand,decidedtocontinuethesoapopera(肥皂剧).