1 . 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以下作文。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：在缺词处加一个漏字符号（∧），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：在错的词下画一横线，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。

The Great Wall is not only regarded as the symbol of China for its historically value, but is also known as one of the Seventh Wonders in the world. With a long of 21, 000 kilometers, it wind up and down across deserts, grasslands, mountains and plateaus. For thousands of years, it serves as a great defence work, keeping enemy away from the northern border. So nowadays it has become a place of interest, attracting visitors from at home and abroad. A tour along the Great Wall will enable you feel the wisdom of the ancient Chinese and the thousands of years changes.