Question

b marks what structure? purkinje fibers sinoatrial (sa) node common bundle atrioventricular (av) node

Explanation:

The atrioventricular (AV) node is located near the center of the heart, between the atria and ventricles. It receives electrical impulses from the atria and transmits them to the ventricles, coordinating the heart's contractions. In the given diagram, the structure marked B is consistent with the location of the AV node.

Answer:

atrioventricular (AV) node