On the door pinned a note,_____ “admission by invitation only”.A.says B.written C.reading D.said为什么选c

On the door pinned a note,_____ “admission by invitation only”.
A.says B.written C.reading D.said
为什么选c

C.reading 这是现在分词作非限制性定语 修饰a note
原句等于 a note was pinned on the door and it reads .