The parties to government procurement refer to the principal entities of all kinds that enjoy rights and undertake obligations in government procurement, including the procuring entities,the （ ） and the procuring agencies.

A、users 

B、servers 

C、producers 

D、suppliers

参考答案：D

参考解析：政府采购当事人是指在政府采购活动中享有权利和承担义务的各类主体，包括采购人、供应商（suppliers）和采购代理机构等。选项A为用户，选项B为服务器，选项C为生产者。