Bob Gates, Aged 16, Looks 19

Multiple Choice

Bob Gates, aged 16, looks 19. He is also mentally incompetent, but it is not obvious that he is. Bob buys a top of the line computer from a salesperson, who has no idea that he is under age and incompetent. Bob paid $3,800 cash for the computer. On what grounds can Bob cancel the contract?

A) Mental incompetency alone
B) Because he is a minor
C) Because he paid cash for the computer
D) Both A and B
E) A, B and C