一句话改错!高三老师看下!

其实都可以

必须加the
是因为all over the world 做后置定语修饰people，这时候人们这个词是特指的，指世界的各地的人们，特指时the怎么能省哪？

都可以啦

我也这么认为。。。
It is a slogan that conveys the lofty ideal of people in Beijing as well as in China to share the global community and civilization and to create a bright future hand in hand with people from the rest of the world.

it has become a place of interest to the people all over the world.

你的老师看的是所谓的标准答案吧，这个地方的定冠词是要去掉的，all over the world 已经表示出全世界所有的人了，哪还有什么特指可言呢，不过有的题目就是那么没有道理，还要你按他们的思路来。