ПОМОГИТЕ ПОЖАЛУЙСТА!! Нужно ставить в место пропуска: can (can't), could (couldn't) или to be able to!!

ПОМОГИТЕ ПОЖАЛУЙСТА!! Нужно ставить в место пропуска: can (can't), could (couldn't) или to be able to!!16. I... buy that book because T didn't bring any money with me. 17. I'm sorry, but I won't .... come to the party on Saturday. 18.I... finish all the work vou wanted me to do yesterday. 19. The manager wasn't in the office for very long, but we .... to speak to him for a few minutes. 20. On entering the house I... smell something burning in kitchen. 21.I'am usually very good at tennis, but yesterday I.... beat my brother. 22. When we lived on the coast, we .... swim in the sea every day. 23. If you don't tell me what your problem is, I... help you. 24.I got home early last night, so I .... watch my favourite programme on TV. 25.1... eat anything when I was younger, but now I have to be more careful. 26. Fortunately he .... convince the police that he was innocent. 27. Smoking.... lead to serious illneses. 28. If I pfss my exam I... study a secretarial course next term.