Nano Corporation Offers to Sell a Robotic Device to Opal

Nano Corporation offers to sell a robotic device to Opal Assembly, Inc., but mistakenly transposes some of the digits in the price so that $15,400 appears in the offer as $14,500. Opal accepts the written offer.
-Refer to Fact Pattern 13-1.Nano's best defense against enforcement of the contract is that Opal knew

A) a bilateral mistake supports the cancellation of a contract.
B) a mistake of value supports the cancellation of a contract.
C) a unilateral mistake supports the cancellation of a contract.
D) the price was below the prices of comparable devices.