A company decides to reduce the number of salespersons in order to weather the temporary economic crisis. The company's board of directors plans to fire the less efficient salespersons first, instead of simply deciding which ones to fire based on the number of salespersons. Which of the following is a prerequisite for the company's board of directors to make this decision? ['The remuneration of the salesman is determined by the amount of business.', 'The salesperson with the most business experience is the best salesperson.', 'One salesperson will not be as efficient as another salesperson.', 'The board of directors has a method to determine the efficiency of the salesman more accurately.']