The story (he told)us last night is very interesting 为什么不用that was told或which he was told?

that 和which 是用于连接两句句子. 但这句本身就是一个完整句子,而且清晰表达意思,没有必要再用连接词.
两句句子: The story is very interesting. He told me that story last night. 把这两句句子连接起来 就变成 : The story that he told me last night is very interesting. 但在此句子中,that 这个连接词并不是必须的,句子的前后关系很明确,而且是个短句子. 所以 that 用不用都可以.
但如果在这个句子中再多加一层意思,那么就需要用连接词了. 比方说,我们要再这个句子中加入对这个故事的描述: The story he told me last night which is talk about the World-War-II is very interesting. 在这句中,which 就是不可省略的了, 他连接了两句句子,把他并成一句. 如果没有which,这句子就只能分成两句来讲. which that when who whom whoes where 都是连接词, 只有当他们在句子中不能被省略时,使用才有意义,否则就不需要用...就像你说的句子,是可以不用的.
另外, that was told 这个用法不准确, was 是"linking verb" ; told 是"verb" 一句句子中, 不能出现两个动词. 你可以说 that told , that was ,但that was told 的用法不正确...换成句子, The story he was told me last night. 就是个病句了,
我不会讲那么多专有名词来解释,这是我自己的一点经验啦...希望有用.