A line segment on a coordinate plane has a slope of 1 and the end points at (1,a) and (9,b). Two points on this line segment partition it in a ratio of 1 : 3 and 3 : 1. Which of the following are the x coordinates of these two points A: 2
B: 3
C: 4
D: 5
E: 6
F: 7
G: 8