the prisoners were let go let变被动 不是要加上省略的to吗 为什么这个句子不加

let 的用法
1）当let后只有一个单音节动词,变被动语态时,可用不带to 的不定式.例如：
They let the strange go.他们放陌生人走了.
---> The strange was let go.
2）当let 后宾补较长时,let 通常不用被动语态,而用allow或permit 代替.例如：
The nurse let me go to see my classmate in the hospital.那护士让我去探望住院的同学.
----> I was allowed / permitted to see my classmate in the hospital.

你是想说为什么不写成the prisoners were let to go吗？这怎么可以？
比如see，see sb. do，to被省了；see sb. doing。
I saw him enter the room。我看见他进入了房间。
变为被动的时候要把省略的to补回来，
即He was seen to enter the room。
let go本来...

常用的不能加to 动词不定式的动词： see /watch /observe /notice /let /make / feel /help
死记就可以了