这个问题还真不太好回答.
被动语态和系表结构没有可比性,也不会混淆的.
例如：
A tree was planted by him yesterday.
这是被动语态.
A tree 是主语,was planted 是谓语,him 是介词by 的宾语,yesterday 是时间状语.
He was happy yesterday.
这是系表结构.
He 是主语,was 是系动词,happy 是表语,yesterday 是时间状语.