帮忙分析一下下面这个句子的语法
Participants in this enterprise were supplied with bicycles,which they used to deliver parcels and messages,and wich they were required to pay for gradually from their wages.这里的which 应该就是定语从句的先行词了,但是在从句中做什么成分呢?宾语的话也有点别扭啊?