Where Two Parties Contract for the Purchase and Sale of an Ordinary

Where two parties contract for the purchase and sale of an ordinary item,such as a desk,that unknown to both parties is a rare and valuable example of that item,this is:

A) A unilateral mistake.
B) A case of fraud in the inception.
C) A mutual mistake of fact.
D) A mistake of value,but not a mistake of fact.
E) A case of fraud by concealment.