Which of these sentences is punctuated correctly?
Did you know (I didn't realize it until I started this paper) that this poem is often quoted?
Did you know--I didn't realize it until I started this paper, that this poem is often quoted?
Did you know--I didn't realize it until I started this paper--that this poem is often quoted?
Did you know, I didn't realize it until I started this paper that this poem is often quoted?
