Here's why:
* Subject-verb agreement: The verb in a sentence must agree with its subject in number (singular or plural).
* Listing items creates a plural subject: When you list items, they are considered a plural group.
Example:
* Correct: "The apples, oranges, and bananas are on the table."
* Subject: apples, oranges, and bananas (plural)
* Verb: are (plural)
* Incorrect: "The apples, oranges, and bananas is on the table."
Exceptions:
* If the listing is treated as a single unit: "The apples and oranges combination is delicious."
* If the listing refers to something singular: "The apples and oranges mix is on sale."