The probability of an event must be between 0 and 1 (including 0 and 1 both). Since 33% is equal to 0.33, it is between 0 and 1, thus it is a possible probable event. -1.5 is not between 0 and 1. The next option is between 0 and 1.
0 can also be a possible probable event. The next option is also between 0 and 1 which can be probability of an event. But the last option is not between the range of 0 and 1, thus can not represent probability of an event.