<image>Given the following four propositions:
① "Putting three balls into two boxes, there must be one box with more than one ball" is a certain event.
② "When x is a certain real number, it can make " is an impossible event.
③ "It will rain in Shunde tomorrow" is a certain event.
④ "Drawing 5 defective bulbs out of 100 bulbs" is a random event.
The number of correct propositions is _______________________________________________ (____)