Continuation from my other question: if we were asking as a question, 'みたことがありますか。' Can we use the question はparticle interchangeably? Or which to use under which circumstances? Thanks!
I think the question is clear enough, although there is no specific context.
I don't know whether all the questions about は/が should be regarded as "duplicated questions." If so, I had better not write this. But anyway, I will try to answer it.
Now I think that the both of は and が are almost completely interchangeable and have the same meaning, in general.
The choice depends on each concrete context. It depends on other grammatical rules.
a and b are completely the same and it depends only on the speaker's preference.
I believe not a few Japanese would choose d, because c includes the double "は" s which seem less natural to native-Japanese speakers' ears.
Hope this helps!