如題，網(wǎng)站沒有修改過任何東西，突然出現(xiàn)

Fatal error:  Call to undefined function Think\C() in /www/wwwroot/www_XXXXXXXl/Include/Library/Think/Think.class.php on line 313

請教各位大大，應該怎么處理才可以正常恢復啊？