Hello!! :)
Your verb is the action in the sentence and you predicate is one of the two main parts of the sentence. And that would be the verb predicate. A participle is used to modify. So lets look at the sentence and pick them out!
Cautiously, the boys CREPT toward the CLOSED door.
Verb: crept Participle: closed
I hope this helped, let me know if you need anymore help or further explanation! :)