or和either的用法区别

　　Do you want one or two?

　　你要一个还是两个？

　　The operation could prolong his life by two or three years.

　　这次手术可使他多活两三年。

　　Well, I think she's either Russian or Polish.

　　嗯，我看她不是俄罗斯人就是波兰人。

　　There is a large window on either side of the front door.

　　前门两侧各有一个大窗户。