请英语语法高手帮忙
1. The book was sent to me by him
“..to me by him ”to me 为什么不放在 by him 后面.
2. The letter was being written by me when you came.
“..by me when you came”为什么when you came不在by me 前面呢?
3. I have been helped by him all my life.
“.. by him all my life”为什么all my life不放在 by him前面?
请问像 By这样的介词位置放在哪里有什么规则吗? 有时候用起来有点模糊.请高手帮忙分析,要具体的讲解哦,不要复制->粘贴的（我看都不看）. 让我能彻底明白的追加100分.谢谢