In English, the word "case' can mean different things in different contexts.
"Case" can mean a container, such as a box or a bag.
"It is my case" could be a shorter way of saying "It is my briefcase" and "It is my suitcase" when you already know from the context of the discussion that you're talking about a briefcase or suitcase.
"Case" is a general legal term for a lawsuit, trial or legal matter.
Here are some examples of the use of the word "case" in the legal context:
- "civil cases" and "criminal cases"
- "case law" = reported court decisions
- "case law" is also law made through court decisions in contrast to law made by statutes
I don't know what Duo expects. Duo teaches everyday English, so it's better to choose ordinary words than specialized words.
Sometimes the subject area can guide you (e.g. "food"), sometimes not ("abstract objects").
Sometimes Duo teaches a use of the word that is unrelated to the subject area.
- For example, in a Spanish lesson on Dates & Time the word "estación" means "season" in most exercises. But there is an exercise in which "estación" means "station" (e.g. train station).
- Similarly, under "Voyages" in English for French speakers, there is an exercise that teaches contrasting uses of the word "ailes"/"wings": airplane wings, (the food) chicken wings.
By the way, I think that I commented on the sentence "It is my case" / Answers: "C’est ma caisse" "C'est mon cas" under the subject area "Objets Abstraits 1".
I think that "the case" / Answer "le cas" is a new exercise.