the problems that our world faces

“that our world faces”是个定语从句，从句中“our world”作主语，应为单数形式。

应该是

the problems that our world faces

在这句话中，主语是‘our world’，which is in singular form; therefore the verb going after this should be also be in singular form.

我是英语老师，帮帮你。
the problems that our world faces
face 的主语是单数名词our world，所以，谓语动词当然用第三人称单数。
祝你进步！

应该是第一句:the problems that our world faces
翻译出来是:全世界都面临的问题
our world作主语,是单数,因此face应该用复数形式:faces
还可以写成:the problems facing our world

主语world为单数 应该用faces 单三

（problems 复数，不要加定冠词the ; face 用分词式;不必加that.按你的中文直译，就成中式英文了），应写成：
Problems we've been faced in the world ; 或 Problems our world would be faced .