4. What is an advantage of genetically engineered biological pacemakers over electronic pacemakers? A) Biological pacemakers have been used much longer than electronic pacemakers.

B) Biological pacemakers inject cells into the patient rather than use surgery to insert an electronic pacemaker.

C) Biological pacemakers can be removed when they are no longer needed, but electronic pacemakers can never be removed.

D) Biological pacemakers work on all patients, but electronic pacemakers only help those patients who have had heart attacks.