Which of the Following Situations Appears to Involve a 'Mutual

Which of the following situations appears to involve a 'mutual mistake'?

A) X purchased goods on credit from Y,believing Y to be Z.Y was aware of X's mistake.
B) A beneficiary and an insurance company negotiated a life insurance policy,both unaware that the subject of the life insurance policy was in fact already dead.
C) Two parties agreed to send goods by a particular ship but there were two ships with that name and each party was thinking of a different ship.
D) X,who spoke little English,signed a document granting Y an option,believing it to be a receipt.This belief was encouraged by Y.