Not necessary, because the conclusion concerns only “many” of the lowest-paid corporate employees. The author isn’t committed to any belief about “all” of the lowest-paid employees.

Not necessary, because if it were not true — if every executive who cuts the pay of the lowest-paid employees does NOT earn less than 50 times what those employees earn — that’s consistent with the author’s reasoning. By implementing a maximum wage law, we can remove the incentive of those executives to lower wages.

Not necessary, because the argument doesn’t concern whether executives will “raise” wages. It’s about whether executives would lower wages for certain employees if there were a maximum wage law.

Not necessary, because the author doesn’t have to believe that executives would “never change the wages” of the lowest-paid employees. If some executives chose to raise wages of employees in order to increase their own maximum salary, that doesn’t undermine the author’s reasoning. In addition, the conclusion asserts only that “many” employees’ wages would be protected; there can be some executives who would still cut some lowest-paid employees’ wages.

Necessary, because this is the link from the premise to the conclusion. The author believes if a maximum wage law were enacted, then at least one executive would refrain from cutting the wages of the lowest-paid employees. You can also think in terms of negation. If (E) were not true — if EVERY executive WOULD CUT the pay of lowest-paid employees even if there were a maximum wage law — then the argument doesn’t make sense. The passage of the wage law would not guarantee protection of many lowest-paid employees’ wages.