[典例1] (2015·江苏高考·B)In the United States alone，over 100 million cell－phones are thrown away each year.Cell－phones are part of a growing mountain of electronic waste like computers and personal digital assistants.The electronic waste stream is increasing three times faster than traditional garbage as a whole.
Electronic devices contain valuable metals such as gold and silver.A Swiss study reported that while the weight of electronic goods represented by precious metals was relatively small in comparison to total waste，the concentration (含量) of gold and other precious metals was higher in so－called e－waste than in naturally occurring minerals.
