Select perpendicular lines from the given pairs of lines :

Select one:

a.
y = 2x + 3, y = 2x + 7


b.
y = x / 2 + 3, y = − x / 2 + 7


c.
y = 2x + 3, y = − x / 2 + 7


d.
y = 2x + 3, y = x / 2 + 7