2017 大数据 大会:post a letter可不可以改成send a letter?两者有何不同？

post a letter可不可以改成send a letter?两者有何不同？ as a scratching post A letter from Jenny open a letter a letter of comgratulage we had a letter from Jill yesterday .可不可以换作had got It was a red letter day in the history of our school. What's the Chinese for“a red letter day”? He's a good teacher.改成复数怎么改 Which letter is a drink? What letter is a drink?