Where to use "must/should/might/may/could/shouldn't have "in a sentence?

We had in our book that "must+perfect infinitive" is used when we feel sure about sth in the past.And "might/may/could+perfect infinitive" should used when we think sth was possible but we aren't sure.And we should use "should+perfect infinitive" when we talk about past events that did not happen.

Now we had exercises about choosing them.Now I have some question.

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> 1.How can we decide which one is "may/might/could+perfect infinitive" when they are the same?
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> 2.We had an exercise "Nobody answered the phone at the clinic.It................ closed early"
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> Here the answer written is "must have" instead of being probable we aren't sure then why did we use it?
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> And also we had "Sarah looks really pleased with herself.She ...............passed her driving test this morning" which gives the answer "must have"but we aren't sure.
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