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.