Hello, thank you for taking the time to post your question!
Do you have any more context for your question? I think the best choice out of the list of options would be “were” just from a subject-verb agreement perspective. (A) and (C) definitely don’t work … (B) possibly works if it’s meant to be a present tense question. But I think that (D) were is the best choice out of the list of options.
Hopefully that gets you moving in the right direction! Feel free to reach out for a lesson if you have any questions beyond that! :)