A nurse who provides care in a geriatric subacute medicine unit of a hospital has noted that a large ...

A nurse who provides care in a geriatric subacute medicine unit of a hospital has noted that a large number of patients receive -adrenergic blocking medications such as metoprolol.
 
  Which of the following statements best conveys an aspect of the use of beta-blockers?
  A)
  They can be used to treat supraventricular arrhythmias and decrease automaticity by depressing phase 4 of the action potential.
  B)
  They inhibit the potassium current and repolarization, extending the action potential and refractoriness.
  C)
  They counteract arrhythmias and tachycardias by increasing vagal stimulation.
  D)
  They decrease myocardial oxygen demand by blocking the release of intracellular calcium ions.