题目

  When you make a mistake, big or small, cherish it like it’s the most precious thing in the world. Because in some ways, it is.   Most of us feel bad when we make mistakes, beat ourselves up about it, feel like failures, get mad at ourselves. And that’s only natural: most of us have been taught from a young age that mistakes are bad, that we should try to avoid mistakes. We’ve been scolded when we make mistakes—at home, school and work. Maybe not always, but probably enough times to make feeling bad about mistakes an unconscious reaction.   Yet without mistakes, we could not已知ab=cd，则下列式子中正确的是（　　）A．a：b=c2：d2B．a：d=c：bC．a：b=（a+c）：（b+d）D．a：b=（a-d）：（b-d）