Question

How do you know if two line segments are parallel?

Answer 1

For this case we have that by definition the equation of a line in its generic form is given by:

$y = m1x + b1\\y = m2x + b2$

Then, by definition, when the lines are parallel, their slopes are equal. This means that it is met:

$m1 = m2$

The lines can have the same or different intersection with the vertical axis.

Answer:

D. Their slopes are equal

Answer 2

D is correct.This is because these lines will never intersect
Their slopes are equal
Their slopes are the same!