The list that finishes the sentence needs to have its three parts, "engaged" and "alert" and "interested," separated by commas. There are no other corrections that need to happen in the sentence. This makes the correct answer choice "to keep an audience engaged, alert, and interested."

A list like the one presented in the underlined portion of the sentence needs to be separated somehow, usually by commas. The only choice that appropriately separates the three items is "plenty of medicine, snacks, and water," which is the correct answer.

The three items in the list of the underlined portion of the sentence, "thoroughbreds" and "Arabians" and "saddlebred horses," are lumped together in one large pile. All such lists need to be separated by commas, to show the separate items clearly. The only answer choice that correctly does this is "between thoroughbreds, Arabians, and saddlebred horses."

A list like the one that makes up the object of the underlined phrase must be have its items appropriately separated by commas, which the sentence does not do as it is written. The only answer choice that correctly separates the three items by using commas is "with a style that was outdated, stale, and unsatisfying."

The underlined portion of the sentence includes a list of three items. All such lists must have the items in them separated in some fashion; therefore, the correct answer is "including television, advertising, and social media."

The list that is the subject of the sentence contains three separate elements, but only appropriately separates two of them. All lists of three or more elements need to have commas between each component. The only answer choice that appropriately does this is "Reading, writing, and arithmetic have."

Use a comma to separate the introductory phrase "In many thrilling mystery novels" from the independent clause that in this case makes up the rest of the sentence, "the good guy actually turns out to be the bad guy."

The phrase "always careful with his words" is an interrupting phrase, one that adds information to the sentence, but remains apart from its structure. All interrupting phrases must be set apart from the rest of the sentence by commas. "The coach, always careful with his words, intentionally avoided" is the only answer choice to appropriately use commas around the interrupting phrase.

The words "a long time activist" are an interrupting phrase, that is a phrase which interrupts the sentence and is not necessary for proper sentence construction, but does provide information. Such phrases must be set off by commas on either end, so "leader, a long time activist, urged" is the best choice among the answers.

The phrase "annoyed with her class" is what is known as an interrupting phrase. An interrupting phrase provides information, but is not necessary to the construction of the sentence. All interrupting phrases need to be set apart by commas, making "The teacher, annoyed with her class, got emotional" is the correct answer.