Which of the following is true of the comparative study by Segall and colleagues between the Mueller-Lyer illusion and horizontal-vertical illusions?

a) The horizontal-vertical illusion was only limited to the primitive groups.
b) The horizontal-vertical illusion was only limited to the industrialized groups.
c) The Mueller-Lyer illusion was stronger for the non-industrialized groups.
d) The Mueller-Lyer illusion was stronger for the industrialized groups.

d