Final answer:
Reducing operating costs as a percentage of sales directly increases a company's profit margin, which measures profitability by comparing net income to sales. The correct answer is option A.
Step-by-step explanation:
Reducing operating costs as a percentage of sales will increase profit margin. The profit margin is a measure of the profitability of a company and is calculated by dividing net income by sales. By reducing operating costs, a business is able to lower its expenses without affecting its sales, thereby increasing the net income and consequently the profit margin. This does not directly increase investment, turnover, or return on investment, although a higher profit margin could indirectly lead to these outcomes over time if the additional profits are strategically utilized.