The point (2, 1) is the midpoint of a line with endpoints at (C5, 3) and:

The point (2, 1) is the midpoint of a line with endpoints at (C5, 3) and:
A . (C3, 4)
B . (C7, 2)
C . (7, 1)
D . (9, C1)
E . (C10, 3)

Answer: D

Explanation:

The midpoint of a line is equal to the average x-coordinates and the average y-coordinates of the line’s endpoints:

(C5 + x) / 2 = 2, C5 + x = 4, x = 9

(3 + y) / 2 = 1, 3 + y = 2, y = C1

The other endpoint of this line is at (9, C1).