The correct answer is C. Class president Alex Kim says, "I was able to arrange for food trucks to come to school during testing week."
Step-by-step explanation
An expository essay is a text that, as its name indicates, has the purpose of exposing the reader to aspects related to a topic to demonstrate what it is about, how it works, its objectives, among others. In the case of an expository essay on school governance and its benefits, the most appropriate supporting detail would be "Class President Alex Kim says," I was able to arrange for food trucks to come to school during the week of tests." Because it is an argument that supports the main topic, and also exposes a verifiable fact related to this topic. Therefore, the correct answer is C.