简述“劣币驱逐良币”的现象。

完形填空
     As she waited at the edge of the ice for her music to start, Peggy took a quick look at her father standing nearby with a group of parents and teachers. He smiled at her. Then she _1_ out at the audience, _2_ to see her mother. These two, Alvert and Doris Fleming, had _3 _all the way from California more than 2,000
miles away, to see their _4 _compete in this sports meet in Cleveland, Ohio.
     The music _5_ and Peggy moved onto the ice, letting the music _6_ her along into her turns, and she
began skating with much _7_ in herself. The cold fear she always had in the _8 _ seconds before skating
onto the ice was _9_ . She was feeling the movement of the _10_ and letting it carry her. She skated
easily, _11_   did some jumps, a final turn and her performance was _12_ .
     The crowd loved it and cheered _13_ she skated off the ice. "Nice job," said one of the other _14_  . It was the remark(话语) that _15_came after a free-skating performance. But what should the _16_ say?
Standing beside her father, Peggy _17_ for the scoring(打分) to be finished. On all sides were other young
skaters, some waiting _18_ alone, others with a parent. Shortly before 10 o'clock the results were  _19_  . The new United States Women's Figure Skating Champion was Peggy Fleming of Passdena, _20_ .