The three experimental questions were added to see how the questions might fare and could possibly be used in future CSSA exams. There is no way to distinguish them and there is no credit given to the questions. You don't receive any credit positive or negative when answering these questions. They will not figure in to your final score.
The multiple response questions, you will get a list of possible answers and the question will ask you to pick two, three or four from the possible answers. If you get one of the answers incorrect you will miss the entire question.
In addition there are also T and F questions on the exams.