ctor must be _______ 24 hours a day, 7 days aweek in the boarding school.

e arguing on who, on earth, is knownfor the great discovery penicillin,an effective bacteria killer.

The Spring Festival, a traditional Chinese festival, is a time of getting together, when people return home from different places and enjoy the _______ of family members.

Paula is pleased that she _________ her lost watch.

ve to stop talking here outside ,Listen,!—Hurry up ,or we’ll be late .