the building model has over pass the status of diversity.k say two rubbish question which makes me confused even l accused about don't know the expand form s first one s number is zero.l don't accept it.besides l was assigned to illustrate a question.get conclusion similar to reflect public knowledge. I try to explain in this way.one room shape is reflected on a plain it become a photo .if it is opposite it will in a point.through this point.lineof this specific plain will associated with the room