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Why am I wrong in the third sentence? Can you explain it to me?

3. Louisa is still in Palma, so you -------------her at the library.

Options:
mustn't have seen
weren't able to see
can't have seen
couldn't see

Apparently the situation is something like this:
A: I saw Louisa today. She was in the library.
B: I think you are mistaken. Louisa is still in Palma, so you can't have seen her there.

The natural American English answer "couldn't have seen" is not one of the options.
"Can't have seen" is the correct usage in British English. It is also used in American English.
As an American, I do use "mustn't have" + past participle, but the Brits do not use the negative form, only the positive (eg. You were there. You must have seen it. / You weren't there. You can't have seen it.)

The others are possible, but in a different scenario:
I couldn't see (meet) Louisa at the library today. She is still in Palma.
I wasn't able to see (meet) Louisa at the library today. She is still in Palma.
cool! i scored 4/6
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"...so you can't have seen her..." ?!
I could swear it should be "couldn't have seen her".
Could you explain the correct answers and why should we choose them ?
Question number 4 is grammatically incorrect. It should be Whose keys are these?
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jaca"...so you can't have seen her..." ?!I could swear it should be "couldn't have seen her".
I agree to this. can't have seen her just doesn't sound right.
CozyI agree to this. can't have seen her just doesn't sound right.
But it is used. See the examples (further down the page) here: http://www.englishgrammarsecrets.com/couldhave/menu.php

and here: http://www.perfect-english-grammar.com/modal-verbs-of-probability.html

We can also use 'can have' to speculate about what has happened but only in questions and negative sentences and with words such as 'hardly', 'never' and 'only'.
You must have misunderstood my comment.
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CozyYou must have misunderstood my comment.
Can't you have implied by your comment that "can't have seen" was not correct?
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