The correct pathway of the impulse of heartbeat through the heart is ...........

• A
  $AV$ node $\rightarrow$ Bundle of His $\rightarrow$ $SA$ node $\rightarrow$ Purkinje fibers $\rightarrow$ Heart muscles
• B
  $AV$ node $\rightarrow$ $SA$ node $\rightarrow$ Purkinje fibers $\rightarrow$ Bundle of His $\rightarrow$ Heart muscles
• C
  $SA$ node $\rightarrow$ Purkinje fibers $\rightarrow$ Bundle of His $\rightarrow$ $AV$ node $\rightarrow$ Heart muscles
• D
  $SA$ node $\rightarrow$ $AV$ node $\rightarrow$ Bundle of His $\rightarrow$ Purkinje fibers $\rightarrow$ Heart muscles