Final answer:
The correct punctuation for the sentence is September 11, is a day that everyone will remember.
Step-by-step explanation:
The correctly punctuated sentence is OC. September 11 is a day that everyone in the U.S. will remember. In this sentence, the comma is not needed between the month and day, as they form a single date. However, it is correct to use a comma after the day and before the year. So the sentence should be: September 11, is a day that everyone in the U.S. will remember.
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