题目

 Lucas        when his mother came back from work.    A. was cried          B. cried           C. is crying        D. was crying 答案：D. 当他母亲下班回来时他正在哭。一物体放在凸透镜的主轴上，从距凸透镜光心1倍焦距处，物体沿主轴移到4倍焦距处，则物体和它所成的像间的距离（　　）A．一直变大B．一直减小C．先变小后变大D．先变大后变小