Which punctuation mark correctly completes the sentence: "Mr. Harris announced to the class, 'Everyone is expected to do the following __ sit quietly, raise your hand before speaking, and participate in discussion.'?"

The use of a colon in this sentence is appropriate because it introduces a list that follows the introductory clause. The structure of the sentence presents the speaker's announcement, and after that, the list of expectations for the class is provided. A colon is specifically designed to signal that what follows will elaborate or clarify what has been mentioned before, which aligns perfectly with the context of Mr. Harris outlining his expectations.

In this case, the colon effectively sets up the three specific tasks that the students are expected to follow. Each item in the list is directly related to what Mr. Harris just stated, making the colon the ideal punctuation mark to use here. It serves to prepare the reader for the expected actions that are to be listed, creating a clear and formal structure for the sentence.