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B is corrent. An oral agreement modifying an existing contract for the sale of goods needs no new consideration to be binding. If the contract, as modified, is for the sale of goods for a price less than $500, the Statute of Frauds does not apply, and the oral modification is enforceable.
A is incorrect. An oral agreement which waives a non-breaching party’s rights arising out of a breach of contract requires consideration to be enforceable.
C is incorrect. The parol evidence rule stipulates that a written agreement intended to be the complete and exclusive agreement of the parties may not be contradicted by prior or contemporaneous oral evidence.
D is incorrect. A firm offer made by a merchant to hold an offer open for a stated period of time without consideration must be in writing and signed by the merchant.