Which of the Following Situations Appears to Involve a 'Common

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

A) 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.
B) X, who spoke little English, signed a document granting Y an option, believing it to be a receipt. This belief was encouraged by Y.
C) X purchased goods on credit from Y, believing Y to be Z. Y was aware of X's mistake.
D) 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.