罗推尔将控制点分为两类（）和外在控制点。

Although custom prosthetic bone replacements produced through a new computer-aided design process will cost more than twice as much as ordinary replacements, custom replacements should still be cost-effective. Not only will surgery and recovery time be reduced, but custom replacements should last longer, thereby reducing the need for further hospital stays.
Which of the following must be studied in order to evaluate the argument presented above

A．The amount of time a patient spends in surgery versus the amount of time spent recovering from surgery.

B．The amount by which the cost of producing custom replacements has declined with the introduction of the new technique for producing them.

C．The degree to which the use of custom replacements is likely to reduce the need for repeat surgery when compared with the use of ordinary replacements.

D．The degree to which custom replacements produced with the new technique are more carefully manufactured than are ordinary replacements.

E．(E) The amount by which custom replacements produced with the new technique will drop in cost as the production procedures become standardized and applicable on a larger scale.