下列光现象中，由于光的折射引起的是（　　）

假定英语课上老师要求同桌之间交换修改作文，请你修改你同桌写的一下作文，文中共有10处语言错误，每句中最多有两处。每处错误仅涉及一个单词的增加、删除或修改。

增加：在缺词处加一个漏词符号（∧），并在其下面写出该加的词。

删除：把多余的词用斜线（\）划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1）每处错误及其修改均仅限一词

2）只允许修改10处，多者(从第11处起）不计分。

    With Teachers' Day draw near, I would like to express my thanks to Ms. Li, who taught my English last year.

    At that time, I was having a trouble studying English and my scores fell. Ms. Li encouraged me and tell me her story that she never gave up before her studies didn't go well. She also said that it was necessary to make efforts so that I would not regret waste time. Her words were the best medicine because she stood in her shoes to deal with problems and gave me helpful advices. She didn't simple comfort me. Her teaching methods also worked. It had never occurred me that studying could be so interested until I met Ms. Li.