Question

contains (10, -8) with undefined slope
A) x = -8
B) y = -8
C) x = 10
D) y = 10

Answer 1

(C) is a vertical line going through (10, -8)
(B) is a horizontal line going through (10,-8)
(C) has infinite (and therefore undefined) slope. (B) has a slope of zero.

They are probably expecting (C) as the answer.