Does 3,6-di-X-cyclohexa-1,4-diene have stereo centers? The following question has multiple correct answers:



The book out of which the question is taken  shows that a, b and d are correct answers. 

According to me c should also be correct, as it shows cis-trans isomerism, both X could go to the front (wedge bond), or one could go to the front (wedge) and one to the back (dash bond).  After all geometrical isomerism is also a sterioismersim.
I came to this conclusion considering the definition given on Wikipedia:


  A stereocenter or stereogenic center is any point in a molecule, though not necessarily an atom, bearing groups, such that an interchanging of any two groups leads to a stereoisomer.
Good point. The (c) compound has two tetrahedral stereogenic carbon atoms, with four “substituents”


$\ce{-H}$,
$\ce{-X}$,
$\ce{-CH=CH-\overset{\text{*}}{C}HX-C=C-\bond{...}}$,
and the same one, $\ce{-CH=CH-\overset{\text{*}}{C}HX-C=C-\bond{...}}$ but from the other side, thus with the opposite configuration, or its mirror image.


(‘*’ denotes (the other) stereogenic carbon atom)

They are called pseudo-asymmetric carbon atoms.

A different relative configuration at these two pseudochiral centers leads to these two ‘cis’ and ‘trans’ isomers.

The definition of stereogenic center (for more complete one, see e.g. this answer) is fulfilled.

(Maybe this topic is too early, for this textbook stage, and the author did not notice this complication.)