1 She has been heard to sing this song several times.
2 When did you start / begin to learn English, Hoa?
3 Spending a week in the countryside is very wonderful.
4 The stomachache prevented Mrs. Lan from enjoying the mean. ( prevent + SO/ ST + from + N/Ving )
5 Shall we have something to eat before the show? ( Shall + we + Vinf )