Прочитаем список дел Сары и определим, какие из них выполнены ('DONE'), а какие ей еще предстоит сделать.
Таким образом, задания, которые Саре не нужно делать, это те, которые не отмечены 'DONE' и которые она еще не выполнила.
Заполним пропуски, основываясь на этом:
20. Sarah doesn't have to take cans and newspapers to the recycling centre.
21. Sarah doesn't have to apply to volunteer at the Eco-club.
22. Sarah doesn't have to volunteer at the Eco-club.
23. Sarah doesn't have to clean the local pond.
Ответ:
20. Sarah doesn't have to take cans and newspapers to the recycling centre.
21. Sarah doesn't have to apply to volunteer at the Eco-club.
22. Sarah doesn't have to apply to volunteer at the Eco-club.
23. Sarah doesn't have to clean the local pond.