Exposition, is a literary device that is used in order to introduce background information, in liturature, this can be very helpful when you are reading a text and need information about settings, events, or characters, this can help you predict what is going to happen in the future, therefore i think A) the breaking-off of Louisa and Joe's engagement, for it gives a background to the reader, so they might understand why the situation in the text or writing happened the way it did, leaving readers with more information about the characters as well as giving them a better understanding of the reading. Hope this was helpful, and have a great day!