Select the parallel lines from the given pairs of lines :

Select one:

a.
y = x / 3 + 11, y = x / 2 + 15


b.
y = 3x + 11, y = 3x + 15


c.
y = 3x + 11, y = − 3x + 15


d.
y = 3x + 11, y = x / 2 + 15