Which of the statement$/$s below is$/$are correct:$$

A pareto$-$efficient agreement is$...$

a$)$ an agreement is reached in which both parties reach their aspiration level.

b$)$ there is no other agreement that would make any party better off without decreasing the outcomes of any other party.

c$)$ the agreement reached falls within the positive bargaining zone.

d$)$ the agreement is reached only after parties have exhausted all possible alternatives.