State the location of the $SA$ node and the $AV$ node.

• A
  $SA$ node - Lower right corner of the right atrium
  $AV$ node - Upper left corner of the right atrium
• B
  $SA$ node - Upper left corner of the right atrium
  $AV$ node - Lower right corner of the right atrium
• C
  $SA$ node - Lower left corner of the right atrium
  $AV$ node - Upper right corner of the right atrium
• D
  $SA$ node - Upper right corner of the right atrium
  $AV$ node - Lower left corner of the right atrium