Here's why:
* Predicate: The predicate is the part of a sentence that tells us something about the subject.
* Simple Predicate: The simple predicate is the verb or verb phrase that forms the core of the predicate.
In this sentence, "The early morning" is the subject, and "is a busy time for the school principal" is the predicate. The verb "is" is the simple predicate because it tells us the state of being of the subject (the early morning).