_________, the matter cannot be settled that easily.

The blank requires a sentence-initial discourse marker that conveys regret or an unwelcome reality. 'Unfortunately' is an adverb meaning 'it is unfortunate that' and serves as a standard discourse marker introducing a regrettable statement. 'Unevenly' (adverb of manner) does not fit semantically. 'Unfortunate' is an adjective and cannot stand alone as a sentence modifier. 'Whatever' would not introduce a regretful tone. Therefore the answer is (b) Unfortunately.