Structure of the argument = when the employee morale is undermined the business becomes less profitable, Thus paying senior employees with stock is bad
Conclusion : Paying senior employees with stock is bad
There is obviously some missing information between the fact that "The profitability of a business is reduced by anything that undermines employee morale" and the conclusion that "Paying senior employees with stock is bad"
The assumption is that gap in the argument, therefore the right option will be something like "pay inequality among employees undermines employees morale"
If you move down to the answer choices :
(A) Large income differences between fixed-salary employees and senior staff tend to undermine employee morale. This exactly fits the gap in the argument mentionned above (B)
Reductions in the profitability of a company are usually due to low employee morale.
Whether the company is more or less profitable it doesn't affect the conclusion that paying senior employees with stocks is not good.(C) Business firms that pay senior staff with stock options
are less profitable than other firms.
Same problem as B, we don't really care about the firms profitability, it doesn't affect the conclusion (D) Reducing the difference in income between senior staff and employees paid only a fixed salary
invariably increases a company's profitability.
Same as B and C, it doesn't affect the conclusion(E) Employees whose incomes rise as the profits of their employers rise
are more productive than those paid only a fixed salary.
The employees who are paid with stocks will be more productive. This seems to support the conclusion, however this answer choice doesn't mention anything about the other employees productivity. What if the gain in productivity is comparatively small to loss in productivity of all the other employees not paid in stock ? In this case the conclusion would make no sense. The right answer is A