In some mergers, shareholders stand to gain the most while employees stand to lose the most.
Therefore, the best choice would be:
e. customers; employees
Please note, while "customers" are sometimes affected, "employees" are often the group that might face layoffs or changes in their job structure post-merger. If you intended to focus more specifically on the typical dynamics of mergers involving shareholders and employees, "b" could also be considered, but it does not cover the aspect of customer gain/loss directly.