Which option shows correct comma usage in a series?

The option that demonstrates correct comma usage in a series is the one that includes a comma before the conjunction 'and' as well as commas separating the individual items in the list. In this case, "The items are apples, oranges, and bananas" properly utilizes commas to clearly separate the three items, ensuring clarity and readability.

Using commas in a series helps to avoid confusion about the grouping of items. The inclusion of the serial comma (or Oxford comma) before 'and' is a stylistic choice that can improve clarity, especially in more complex lists. The other options lack proper punctuation or structure, leading to ambiguity or grammatical errors. For instance, omitting any commas at all, as seen in some choices, results in a run-on statement that can make it harder to distinguish where one item ends and another begins.