Question

People work because they need money to live, what

People work because they need money to live, what are some other reasons that people work ?请问最后的work 为什么不是work for?

Answer 1

what are some other reasons /that people work /?
that people work 是定语从句，修饰先行词reasons,that是关系副词，此处相当于 for which。
再如：I don't like the way that he speaks.=I don't like the way in which he speaks.中that就是关系副词，此处等同于in which。
也就是说，在定语从句中，that大多数时候是关系代词，但是也有充当关系副词的时候。
如还有疑问，愿意共同学习探讨。

Answer 2

work for为。。。工作，而这里是人们工作的原因，不是为了原因而工作。如果有for 那变成了 people work for the reasons了

Answer 3

如果有了介词for, 则for 之后必须再跟介词宾语。而这里没有介词宾语，因此就不能用for.