Here's why:
* Predicate: The predicate is the part of the sentence that tells us what the subject does or is. It usually contains the verb and any objects or complements that modify the verb.
* Subject: The subject is the part of the sentence that performs the action or is being described. In this case, the subject is "Rice plants."
The verb "thrive" describes what the rice plants do, and the prepositional phrase "in 4 to 8 inches of water" tells us the conditions under which they thrive.