Walt sells his pickup truck to Bob. When Walt starts to remove its camper shell, Bob says, “Wait. We agreed the camper shell was included.” Walt points to their written contract and says, “No, we didn’t.” The contract says nothing about the camper shell. The camper shell is

a. part of the deal under the parol evidence rule.

b. not part of the deal under the parol evidence rule.

c. part of the deal because Bob thought it was.

d. not part of the deal because Walt thought it was not.