过去分词开头的疑问

retained by.........？还是retained by.....was...？或者是要加个名词在retained by才是对的呢？

retained by... 只是一个过去分词短语。组成句子的话，还需要不少成分。比如：

1. The money was retained by him. （构成被动语态）那些钱由他保留。

2. The money retained by him was lost. （作 the money 的定语） 他保留的那些钱丢了。