Principled negotiation is defined by four points. The following description matches which of these points in the list below? Effort should be devoted to finding a wide variety of possible solutions$$or elements thereof$$that advance the mutual interests of the conflicting parties.

a$.$

Before trying to reach agreement, invent options for mutual gain

b$.$

Insist on using objective criteria

c$.$

Focus on interests, not positions

b$)$ Focus on interests, not positions

d$.$

Separate the people from the problem

e$.$

None of the choices