Which of the following is true of a unilateral mistake?

Which of the following is true of a unilateral mistake?
A) Only one mistake or ambiguity is present in the subject matter of the entire contract.
B) Out of several contracts drafted simultaneously between two parties, one has a mistake in its subject matter that does not concern the other contracts.
C) Only one party is mistaken about a material fact regarding the subject matter of a contract.
D) A single mistake about a material fact in the subject matter of a contract appears several times in the contract.

This is for my business law class, anything will help