Is located closest to the center of heart A)left atrium B)AVnode C) SA node D) atrioventricular bundle.?

The correct answer is C. SA node.

The SA node is located in the right atrium, near the entrance of the superior vena cava. It is the primary pacemaker of the heart and is responsible for generating the electrical impulses that cause the heart to contract. The AV node is located at the junction of the atria and ventricles and delays the electrical impulses slightly to allow the atria to fill before the ventricles contract. The atrioventricular bundle is a group of fibers that connect the AV node to the ventricles and conducts the electrical impulses from the AV node to the ventricles. The left atrium is located on the left side of the heart and receives oxygenated blood from the lungs.