Which sentence uses Carl the Comma correctly? You ate popcorn, hotdogs and French fries, at the carnival. You ate popcorn, hotdogs and French fries at the carnival. You ate, popcorn hotdogs and French fries at the carnival. You ate popcorn, hotdogs, and French fries at the carnival.

The sentence that uses Carl the Comma correctly is:

You ate popcorn, hotdogs, and French fries at the carnival.

Explanation:

A comma is a punctuation mark very often used when listing three or more items.  According to the Oxford Comma grammar rule (sometimes described as the "US comma convention"), a comma must be used before the last list item in a list of three or more items.