The Main Purpose of an Enclosure, Attachment or Link That

The main purpose of an enclosure, attachment or link that accompanies the main letter in a direct message is to:

A) summarize all the information stated in the main message.
B) provide helpful information that does not fit into the main letter.
C) function as the main source of persuading a customer.
D) duplicate and reiterate all the contents of the main letter.
E) enable a reader to reply to the main sales letter.