Choice "B" is correct. A material breach generally will discharge the nonbreaching party. Choice "c" is not as good an answer as "B". While a delay in performance could cause a discharge, it will do so only in a UCC Sales contract, a contract stating that time is of the essence, or if the delay otherwise materially breaches the contract.Choice "d" is incorrect. Generally if a party tenders performance, the other party will also have to perform. Tender of performance does not discharge the other party.
Choice "a" is incorrect. Generally, contracts are assignable, and an assignment of rights will not discharge the other party from performing.