A list like the one in the underlined portion of the sentence always needs to be separated by commas to clearly distinguish between the different elements in the list. The only answer choice that correctly does this is "Rowing, lacrosse, and tennis are," making it the correct answer choice.

The three-part list that is the subject of this sentence does not employ appropriate demarcation between its separate parts. Lists like the one in the sentence need to be separated out by commas to show their individual parts. "Dogs, cats, and small animals have always been" is the only answer choice that appropriately deploys commas in the list.

The list of items that ends the sentence as its object is not properly separated out by commas. Any list needs to have its elements clearly delineated, and of all the answer choices, the only one that accomplishes this is "The school offered programs in engineering, computer science, and architecture."

The underlined portion lists three different things, "the dog," "the cat," and "the rabbit." Each of these needs to be appropriately separated to clarify they are all different. "The dog, the cat, and the rabbit," is the correct answer choice.

The underlined words make up a list. Such lists need to have each element separated for clarity and understanding. "Sailors, marines, and soldiers" is the best choice among the answers.

The underlined phrase contains a series, or a list of grouped items. All series in a sentence must be divided by each other for linguistic and logical clarity. The best way to do this is with commas, making "on supplies, troops, and ammunition," the correct answer.

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."