The official exam will say "Choose 3 correct answers" (at least, the last i heard). if you choose more or less than 3, you get it wrong. if you don't choose the correct 3, you get it wrong. There is no partial credit.
Many practice exams don't tell you how many to choose, just to really make you think about the questions more. They are usually slightly harder than the real exam, or so I am told.
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors