First, in the exercise on the left, choose the correct modal verb in the present tense, in order to construct a text that makes sense. Then, replace the modal verb in the sentences on the right with the correct alternative form in the past tense.
- Tom tidy his office last month because he find anything anymore.must → had to|can → be able to (could is also possible here)
- His boss told him that he be tidier.ought to → be expected to/be supposed to/be to
- Otherwise he work in his department in the future.can → be allowed to/could|To note: since this sentence is referring forward to the future from its standpoint in the past, we have to use the conditional (would not be allowed to|could not)
- When customers wanted information, he be able to help them immediately.ought to → be expected to/be supposed to/be to
- He to keep them waiting.must not → be not allowed to
- As he had sorted the files that morning, he panic when a customer called.need not → don’t have to
- Instead, he help them immediately.can → be able to (could is also possible here)