by the way的by什么词性

by的词性是介词，by the way意思是顺便说一下，例如：

1、What's the time， by the way?顺便问一句，几点钟了

2、By the way， I found that book you were looking for.顺便提一下，我找到了你在寻找的那本书。

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