题目选项分析

Firms adopting "profit-related-pay" (PRP) contracts pay wages at levels that vary with the firm's profits. In the metalworking industry last year, firms with PRP contracts in place showed productivity per worker on average 13 percent higher than that of their competitors who used more traditional contracts.

If, on the basis of the evidence above, it is argued that PRP contracts increase worker productivity, which of the following, if true, would most seriously weaken that argument?

【选项】Because introducing PRP contracts greatly changes individual workers' relationships to the firm, negotiating the introduction of PRP contracts in complex and time consuming.