Manufacturers have learned that consumers place a high value (50) convenience and disposability. Today, many products — such as cans, bottles, paper napkins, and even paper clothing — are designed and manufactured to be used once and then thrown away. Other consumer goods, ranging from wristwatches and umbrellas to major appliances such as air conditioners and VCRs, are manufactured in (51) a way that it is often cheaper and easier to discard and replace them if they break down than it is to have them (52) .A、study showed that 26% of the solid waste that is thrown away in the United States consists of items that are designed to be discarded: disposable diapers, throwaway plastic pens and watches, and the like. A.for B.on C.at D.of