Which of the following cardiac chamber forms the base of the hea?

Posterior surface or base of the hea is entirely formed by the left atrium which receives the 4 pulmonary veins. The anterior or sternocostal surface consist of the right atrium, veical atrioventricular groove, and the right ventricle with a narrow strip of left ventricle appearing on the horizon of the left border.The inferior or diaphragmatic surface consist of the right atrium receiving the inferior vena cava, the anteroposterior atrioventricular groove and to the left this the ventricular surface is made up of one third right ventricle and two third left ventricle separated by posterior interventricular branch of right coronary aery.Ref: Waxman S.G. (2010). Chapter 19. The Limbic System. In S.G. Waxman (Ed),Clinical Neuroanatomy, 26e.