$x \times x \times x \times x \times x \times x$
$x \times x \times x \times x \times x \times x$
$x \times x \times x \times x \times x \times x$
In viewing the items above, seeing three columns of $X$ s on the left versus three rows of $X$ s on the right can be explained by the Gestalt principle of _________.
a. closure
c. proximity
b. similarity
d. contiguity