we should have this letter to be sent.还是we should have this letter send.我觉得是第一种对,可是那是不是就说明have sth to do这种用法不对呢?
网友回答
have sth to do :有一些事需要去做,这里的have是有的意思.
have sth done:有一些事被（别人）做,这里的have是助动词,没有意思.
eg:1.I have some clothes to wash.
2.Can you help me have the clothes washed?
所以,你的第一种用法是错的,应该是：we should have this letter to send.
第二种用法是正确的.
======以下答案可供参考======
供参考答案1:
we should have this letter send.是让别人来做
要看你想表达什么意思,自己做还是让别人做
have sth to do 是有事要做,不一样的用法
供参考答案2:
have sth to be done= have sth done