Andrea, let's look at our options.
a. We know that you don't put a comma between the month and day. You would say today is September, 12.
b. We can use commas to set apart part of a sentence that doesn't necessarily need to be there to complete the sentence. So, this sentence could say, "I took Angie to the movie last night." Because we want to differentiate which Angie, we add, "the one with the freckles," but we need a comma at the beginning and the end of, "the one with the freckles."
c. You use a comma before "and" if you have two different ideas, like "I went to the store, and Joey went home." We also can use a comma before "and" if we have more than two things, like "apples, bananas, and oranges," though the comma is not necessary. Because we only have two people, Jeremy and I, no comma needed.
d. Almost like b, right? We can say, "You are telling the truth." We want to add in something, "I am sure," so we use commas on either end to set it apart.
Your answer is d.