Lu Yumei is nine years old. She is in the third grade. 最近，她所在的上海育辛外来人员子弟小学开了一门新课程：警察叔叔教大家过马路！How funny it is! Every week, policemen come to the school. They teach students how to cross the street. "We play games and sing songs in class. The lessons are interesting and helpful," said Yumei...