题目

 So ________ student ________ that he can work out all difficult problems.    A. clever a ; was he   B. a clever; was he   C. clever a , he was    D. a clever, he was 答案：A下列现象中，由光的折射现象形成的是 ( )A. 日全食B. 树荫下圆形光斑C. 雨后彩虹D. 水中拱桥的倒影