题目

    Store shelves are filling up with so-called “green” products promising to benefit the environment. A recent argument shows that it can be as difficult for buyers to confirm such statement as for producers to defend them.     The argument concerns the Green Plug Electricity Saver. The Green Plug is supposed to prevent energy waste by electrical equipment whose constant -speed motors operate at less full load---as is especially true of older refrigerators. Research showed that such motors can be made to do the same work with less heat, noise, and power consumption just by l 下列函数的表达式中，x均表示自变量，不是反比例函数的是 [　　] A． B． C．y＝ D．xy＝－2