单双买法简介：Old Man Yan was correcting a lot of essays. As he read them, he sometimes nodded with satisfaction, sometimes dumbfounded, sometimes couldn't help laughing, and sometimes shook his head helplessly.
Old Man Yan was correcting a lot of essays. As he read them, he sometimes nodded with satisfaction, sometimes dumbfounded, sometimes couldn't help laughing, and sometimes shook his head helplessly.
