A. increase in number: Cardiac myocytes in the adult are largely terminally differentiated, so they do not appreciably multiply (hyperplasia) in response to increased workload. B. increase in excitability: Increased workload causes structural and functional adaptation (hypertrophy) rather than a primary increase in membrane excitability; excitability changes are more a feature of pathological electrical remodeling. C. decrease in length: Cells do not shorten as an adaptive response to increased workload; they grow (change in size/shape) rather than decrease in length. D. increase in size: Cardiac muscle responds to increased workload by hypertrophy (an increase in cell size) to generate greater contractile force.