Answer:
Quickly.
Step-by-step explanation:
Adverbs are those words that add to the meaning of the verb in the sentence. They are used to make the meaning of the verbs more clearly, adding extra information to the way the verbs are used in the sentence.
In the given sentence,
The school year passed quickly
the verb used is "passed" and the adverb is "quickly" as it gave the added information of how the school year passed.