Question

这个英语句子差什么成分？

I'm told they going by bus, but I would rather they went by train，would后面怎么没有动词，went前面不需要to吗

Answer 1

您好，I'm told they going by bus, but I would rather they went by train.  中差的成分是 going 这个动词，缺少了 were，构成（过去进行时），或是改成（went），这里 went 更好，符合整个句子的语义。所以正确的句子是：

I'm told they went by bu, but I would rather they went by train.

这里的 went 不需要添加 to，因为 went 是（一般过去时），添加了 to，就需要把 went 改成 to go，但如此做，they 后面就缺乏了谓语动词，因为 to go 是（动词不定式）属于（非谓语动词）范畴，所以 went 保留原样。

would rather 是（情态动词），译为【宁愿做某事（也不愿意做其他事）】的用法，后接动词原形，或是接从句结构，所以 would 和 rather 是看作固定搭配。比如：

I would rather go home than to stay here.（我宁愿回家也不留在这里）
I would rather (that) they went by train (than by bus).（原句中的改写）

Answer 2

would rather在这里是一个短语，可以接动词不定式，也可以接一个宾语从句，这个宾语从句前面可以省略that，宾语从句里的动词要用虚拟语气，也就是把时态往前推一级。这种虚拟语气在瑞典语和德语等语言里也存在。