Choice "A" is correct. The monetary unit assumption means that money is the common denominator for economic activity and provides an appropriate basis for accounting measurements and analysis.
Choice "d" is incorrect. The going concern assumption has nothing to do with money per se. The going concern assumption presumes that an entity will continue to operate in the foreseeable future.
Choice "b" is incorrect. The periodicity has nothing to do with money per se. The periodicity assumption is that economic activity can be divided into meaningful time periods.
Choice "c" is incorrect. The economic entity assumption has nothing to do with money per se. The economic entity assumption is that economic activity can be accounted for when considering an identifiable set of activities.