Warning: file_put_contents(): Only 0 of 4986 bytes written, possibly out of free disk space in /home/www/wwwroot/zidian/69228.com/index.php on line 55 国产人与动人物a级毛片,日本按摩高潮a级中文片免费
If I don't show you any argument for v, it means v at time t and the subscript of 0 means t is 0. 如果我不對v做任何標志,那就表示t時刻的速度v,下標0表示的是t=0 耶魯公開課 - 基礎物理課程節(jié)選