Cis and Trans Isomerism given three different groups around the reference plane

In the following problem I am meant to deduce the molecules that are *cis-trans* isomers of each other.
This question does not make much sense in my head because I thought that *cis/trans* isomerism was only applied to configurational isomers if there were only two types of groups bonded to the carbon atoms in the carbon-carbon double bond i.e. the reference plane. Such that, if there are more than two groups bonded to the carbons in the reference plane then *E/Z* isomerism should be used. However, then I thought that *cis/trans* isomerism is a subcategory of *E/Z* isomerism and therefore I tried to work out the solution using the *E/Z* method of finding configurational isomers by finding the relative priorities based on the atomic numbers for the atoms attached to the carbon atoms on each side. Using this method I discovered, that the solution could only be 'A. X and Z' since X seems to be an '*E*' isomer since its high and low priority groups are across from eachother and Z seems to be a '*Z*' isomer since its high and low priority groups are on the same side. 


Am I on the right track? 


[![enter image description here](https://i.stack.imgur.com/RynYg.png)](https://i.stack.imgur.com/RynYg.png)





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> Am I on the right track?
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Generally, yes. For this question, yes but you have over thought this question.


For starters, any answer with Y can be totally eliminated as Y is neither *cis* nor *trans*. Now you are down to answers 'A.' and 'D.'


Here you correctly determined the *E* and *Z* configurations of molecules with identical functional groups, but could have saved yourself some effort if you had recognized W and Z are identical molecules that are inversions/180° rotations of each other. Thus it can't be D. and the answer is in fact:



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> A.
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