Maybe I noticed a small typo

Question

Bonjour Madame Aurélie,While doing a test named “Conte de fées” I landed up at a mysterious sentence -Le père était àgé et sortirait rarement de son lit, alors sa fille devait s’occuper du jardin et des animaux.Here I would like to ask you why a dû was marked incorrect although the English translation specifies ‘so his daughter had to take care of the garden .....’ . I read your lesson which states that one uses Passé Composé for an obligation that was very well met. And here too is the same case.The link to the test -https://french.kwiziq.com/my-languages/french/tests/take/2581800Please help me to figure out the correct option.Merci d’avance ! Bonne journée!

Accepted Answer

In the example you quote, the imperfect is used to indicate that caring for the garden and the animals is a usual action, like a background info. If the passé composé were used, it would be a one-shot deal.