It will be B) because it matches the correct english question tag. If the Option will be A) then the question should be ______ flight arrived now? So, it is incorrect If the Option will be C) then the question should be _____ is your flight's name. Then it is incorrect it is incorrect. If the Option will be D) then the question should be ______'s flight will you come. Then, it is incorrect. So the correct option is B) When.