Final answer:
The underlying assumption of a gainsharing program is collective effort, where employees share in the profits and this typically leads to improved productivity.
Step-by-step explanation:
The underlying assumption of a gainsharing program is b. Collective effort. This type of program is a system where the profits and earnings are distributed among the employees, with the idea that everyone's contribution leads to the success of the business. It relies on the concept that when employees stand to benefit directly from the company's success, this usually results in improved productivity as every individual works towards a common goal. This shared responsibility encourages teamwork rather than individual competition, and it operates outside a traditional hierarchical structure or concerns about employee turnover.