Here are the best answers for each sentence:

1. Cheques are useful **to** travellers.
2. Are you successful **in** your experiment?
3. She got back safe **from** her adventure.
4. It was very lucky **for** me that my bag was found.
5. He seems friendly **to** everyone in the village.
6. She was sad **about** my refusal.
7. Quang Linh is popular **for** folk songs.
8. The student is quick **at** understanding what the teacher explains.
9. The story is very pleasant **to** us.
10. He is very kind **to** me.
11. I’m capable **of** speaking two languages.
12. She is never late **for** work.