A "negotiation" is best described as:

a "zero sum" game between two people with conflicting goals

competitive "haggling" between two or more people in which the only way one person wins is by having the other person lose

a process that helps two or more people work together to achieve goals and solve problems

a problem$-$solving activity that requires the active participation of both negotiators for a deal to be reached.

both and c

both $c$ and $d$