Quadrilateral WXYZ is on a coordinate plane. Segment YZ is on the line x+y=7, and segment XW is on the line x+y=3. Which statement proves how segments YZ and XW are related?
A. They have slopes that are opposite reciprocals of 1 and -1 and are therefore perpendicular
B. They have the same slope of 1 and are therefore parallel
C. They have slopes that are opposite reciprocals of 0 and undefined and are therefore perpendicular
D. They have the same slope of -1 and are therefore parallel