Odpowiedź:
1.The visitors could see the latest exhibition.
(x):The visitors couldn't/could not see the latest exhibition.
(?):Could the visitors see the latest exhibition?
2.We have to watch the weather forecast.
(x):We don't/do not have to watch the weather forecast
(?):Do we have to watch the weather forecast?
3.Derek will be able to meet us at 5.
(x):Derek won't/will not be able to meet us at 5.
(?):Will Derek be able to meet us at 5?