Final answer:
The left atrium's function is to receive oxygen-rich blood from the lungs, which it then sends to the left ventricle.
Step-by-step explanation:
The function of the left atrium is to receive oxygen-rich blood from the lungs. This is accurately represented by option B) It receives oxygenated blood from the lungs. The oxygenated blood reaches the left atrium via the four pulmonary veins after gas exchange has occurred in the pulmonary capillaries.
The left atrium serves as a holding chamber for this blood before it passes through the mitral valve and into the left ventricle. During the cardiac cycle, the left atrium contracts, contributing to the filling of the left ventricle with blood, which is then pumped to the rest of the body.