Question: A and B sign a written agreement, containing only the words "computer" and "$500." Question options: a) Under Williston, parol evidence would be admissible, because the agreement appears incomplete. b) Under Williston, parol evidence would not be admissible, because the agreement contains the required terms and the other terms can be gap-filled. c) Under Corbin, parol evidence would be admissible regarding the intent of the parties to create a complete integration. d) Both (a) and (c).