by the way的by什麼詞性

by的詞性是介詞，by the way意思是順便説一下，例如：

1、What's the time， by the way?順便問一句，幾點鐘了

2、By the way， I found that book you were looking for.順便提一下，我找到了你在尋找的那本書。

3、You could tell she was foreign by the way she dressed.從她的穿着就可以看出她是外國人。