Answer:
d. synergism.
Step-by-step explanation:
Given that the term synergism is a term that describes the process of interaction between two or more parts or groups to give rise to a combined result that is greater than the sum of its parts or groups.
Hence, in this case, when the managers in a marketing department produce a marketing plan that is "greater than the sum of the parts contributed by individual managers," this is an example of: SYNERGISM