Do you know the definition of the probability space?
This forum is starting to get littered with spam.
mathewnaren, the reason emakarov asked that question was that whoever gave you that problem clearly expects you to know what a "probability space" is! And, once you know that, this problem is pretty easy. I will tell you this much: a probability is always between 0 and 1 and all possible probabilities must add to 1.