Here's why:
* Subject: The subject is the person, place, or thing that performs the action of the verb.
* Verb: The verb in this sentence is implied. We can assume the verb is "is" or "will be" (Their family reunion is in July or August, or Their family reunion will be in July or August).
* Subject-Verb Agreement: The subject, "Their family reunion," is singular, and the implied verb agrees with the subject.
Let me know if you'd like to explore more sentence structures!