Question

That's the film I saw it.  That's the film I saw

这个定语从句为什么把it减去了
还有这个句子有好几句都是
They are the thieves the police caught them.
They are the thieves the police caught.

Answer 1

That's The film I saw it. 和 They are The thieves the police caught them. 两句话中的it和 them都应该删掉，因为I saw 和 The police caught 都是定语从句，分别修饰the film 和 the thieves ，关系代词that虽然省去了，但代替它们在定语从句中做成分。如果it和them不删，that就不能作宾语了。

Answer 2

第一个是错的，第二个是对的。因为第一个是个定语从句，定语从句这里省略了关系代词，关系代词就是指的个电影再加这个it就重复了.

Answer 3

英语很简单又直白，尤其是口语上，只要表达清晰，省略的情况很多，例如：I take a walk to school where is nearby of streets.
省略: I walk to school where nearby.