They are often heard __sing_ (sing) in the next room in the morning.
hear sb do sth 听到某人经常做某事
The police_have tried__(try)their best to find these robbers these dsys.
these days是现在完成时态的时间状语。
_To raise_(raise)money for helping poor children ,they organized a charity show.
不定式做目的状语。
1、sing 这里有个often,表示经常性、反复性的,用原形。
2、try “these days”是平常性的,用一般现在时。
3、To raise 动词不定式表目的。
望采纳!