Final answer:
In the sentence, 'John sat between Susan and Darlene,' the word 'between' functions as a preposition, indicating the spatial relationship between John and the two women.
Step-by-step explanation:
In the sentence "John sat between Susan and Darlene," the word between acts as a preposition. A preposition is a word that shows the relationship between a noun or a pronoun and other elements in the sentence, indicating things like location, direction, time, or to introduce an object. The sentence provided demonstrates that John is located in the middle of Susan and Darlene, which establishes a spatial relationship. This aligns with definitions and examples provided in educational resources like Chapter 12, Lesson 2, where prepositional phrases are discussed. It's worth noting that prepositional phrases can never act as the subject of a sentence and can be part of an introductory phrase in a sentence, which sometimes requires a comma.