In Designing Sales Contests to Motivate the Sales Force, Which

In designing sales contests to motivate the sales force, which of the following statements is incorrect?

A) sales contest can help clear an overstocked inventory, smooth out seasonal variations, and train salespeople to sell the entire line.
B) salespeople should be able to identify psychologically with the contest theme.
C) cash prizes are likely to have the most lasting incentive impact on the salespeople.
D) most sales contest last more than one month but less than five months.