一元二次方程x²=4x的根是（    ）

张岂之主编的《中国历史》(辽宋金卷)认为，王安石变法时，国家通过市场的力量调节供需和物价，而不是着重于国家的直接经营活动。相应的变法措施是（    ）

                                                                                    A Nice Clean Plate
   It's Saturday evening. Bruce is having a birthday party. There are a lot of children at the party. They play together for an hour. Then Bruce's mother gives them some food. But she forgets to give Sam any.
   Sam feels wronged(委屈) but then he remembers his mother's words, “Be polite.(礼貌). Don't ask for food.” So he waits for a few minutes, then he holds his plate up over his head and says loudly, “ Does anyone want a nice clean plate?”