they have/were planted last year.哪个正确以及区别.

They were planted last year 正确,此为一般过去式的被动语态,系动词用过去式were,动词用过去分词.整句话意思是他们是去年被种植的.They have planted last year要怎样更改They have been planted last year.用现在完成时态的被动语态是否可加by sb.可以加的, 加上动作的施行者They have been planted last year by xiaoming？加在最后是吧时间状语last year 放最后