题目选项分析

Clearbell Telephone provides slow-dialing (SD) service to customers for a low fee, and fast-dialing (FD) service to other customers who pay a somewhat higher fee. FD technology, however, is so efficient that it costs Clearbell substantially less per average call to provide than does SD. Nonetheless, accountants have calculated that Clearbell's profits would drop if it provided FD to all its customers at the current low-fee rate.Assume that installation costs for FD are insignificant if the customer already has SD service.

Which of the following, if true about Clearbell, best explains the results of the accountants' calculation?

【选项】Profits rose slightly each month for the first three months after FD was first offered to customers, then fell slightly each month for the succeeding three months.