Which of the following statements is false?

Which of the following statements is false?
  a. A heart will stop beating when the nerves to the heart are severed.
  b. Some cardiac muscle cells are self-excitatory.
  c. The pacemaker of the heart is the sinoatrial node.
  d. Cardiac muscles join end to end to allow rapid communication.
  e. Cardiac muscles contract essentially in unison.

Question 2

The structures that connect neighboring cardiac muscle cells to ensure rapid electrical conduction are
  a. desmosomes.
  b. intercalated discs.
  c. synapses.
  d. endothelial cells.
  e. smooth muscle cells.