A agrees to build a machine for B by September $1$ for $$3000\mathrm{.}00.$ On August $15,$ both A and B agree not to proceed with the contract. In this situation,

a$.$

$.$ the contract has been discharged by a condition precedent.

b$.$

the contract has not been discharged and the parties must complete their respective obligations

c$.$

the contract has been discharged by a condition subsequent.

d$.$

the contract has been discharged by anticipatory breach.

e$.$

the contract has been discharged by waiver.