The police still haven't found the lost child, but they're doing all they （ ）.
（A）can
（B）may
（C）must
（D）should
Why didn't you come to Mike's birthday party yesterday? — Well, I （ ）, but I forgot it.
（A）need have
（B）ought have
（C）should have
（D）must have
I love the weekend because I （ ） get up early on Saturdays and Sundays.
（A）needn't
（B）mustn't
（C）wouldn't
（D）shouldn't
