Both the left and right atria receive blood from:

Both the left and right atria receive blood from the veins.

Explanation:

Inside the heart, the atria are the two upper saccular cavities, right and left, separated by a septum (the interatrial septum) and located above the respective ventricles, with which they communicate through each atrioventricular hole endowed with valves.

The right atrium receives the carboxygenated blood that comes from the superior and inferior venae cavae, after having traveled the organism. That blood passes through the tricuspid valve to the right ventricle, which in turn pumps it into the pulmonary artery through the pulmonary valve. In the lungs, that blood is oxygenated and returns to the heart through the pulmonary veins, which flow into the left atrium. Through the mitral valve, this blood passes to the left ventricle and, from there, through the aortic valve, to the aorta, from where it is distributed throughout the body.