The sentence that uses direct address is "Where are you going, Fred?".
Direct address in grammar means that you are speaking directly to a person or group of people either calling them by name, as in example, "Where are you going Fred?", or using the second person pronoun "you". As in the example above, the name is often separated from the rest of the sentence or question by a comma. For example, "Maria, I need you to finish your homework now."
I'm not 100% sure because it's been a while since I have read the book, but I want to say it's B or the second choice given.
The antecedent of "their" is <span>Harvey and Justin.
An antecedent is the word that a pronoun replaces in a sentence. In this sentence, Harvey and Justin are the people who are assembling the tree house, therefore, Harvey and Justin are replaced by the pronoun their.</span>
The prefix would be epi-, as in epidermis. (The outer layer of skin)