"Jack doesn't run as fast as Mark" 是杰克没有马克跑得快的英文表达方式。
这句话的结构是通过对比来表达两个人跑步速度的不同，使用了"as + 形容词/副词 + as" 的结构来比较两者。
例句：
"She doesn't sing as well as her sister." (她唱歌不如她姐姐好。)
"He doesn't speak Spanish as fluently as I do." (他讲西班牙语不如我流利。)
总之，这句话的来源是英语中的比较结构，通过比较来表达两者之间的差异。