请教LAST-9-4-24

请教各位：

该题的答案为什么是C？

24.   Most disposable plastic containers are now labeled with a code number (from 1 to 9) indicating the type or quality of the plastic. Plastics with the lowest code numbers are the easiest for recycling plants to recycle and are thus the most likely to be recycled after use rather than dumped in landfills. Plastics labeled with the highest numbers are only rarely recycled. Consumers can make a significant long-term reduction in the amount of waste that goes unrecycled, therefore, by refusing to purchase those products packaged in plastic containers labeled with the highest code numbers.

Which one of the following, if true, most seriously undermines the conclusion above?

(A) The cost of collecting, sorting, and recycling discarded plastics is currently higher than the cost of manufacturing new plastics from virgin materials.

(B) Many consumers are unaware of the codes that are stamped on the plastic containers.

(C) A plastic container almost always has a higher code number after it is recycled than it had before recycling because the recycling process causes a degradation of the quality of the plastic.

(D) Products packaged in plastics with the lowest code numbers are often more expensive than those packaged in the higher-numbered plastics.（C）

(E) Communities that collect all discarded plastic containers for potential recycling later dump in landfills plastics with higher-numbered codes only when it is clear that no recycler will take them.

文中的结论是，尽量避免使用级数高得塑料以保护环境。

而C说任何一种塑料在循环降解后级数都会升高，那么使用这种级数高的塑料是不可避免的，所以削弱文章结论。

请指教！