"watch sb do"改被动语态时要"sb be（如is）watched to do ".
"find sb do"改被动语态时要"sb be（如is）found to do ".
"help sb do"改被动语态时要"sb be（如is）helped to do ".
“长城闻名于世”：
Grate Wall is well known by people all over the world .
“全世界讲中文的人数最多”：
Chinese is spoken by the most population of the world .