题目

Many people have been ill from a strange disease these days, _____ we’ve never heard of before. A. it      B. that         C. one      D. this 答案：C 解析: 考查指示代词，这里用one指代前面的a strange disease，充当同位语。由发光点S发出的一条光线经平面镜反射后，反射光线将通过A点，试在图中确定这条光线及其反射光线．