This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thorax, Subject name: Anatomy
As viewed from the right atrium, the floor of the fossa ovalis is formed by 
Select and explain. 
A. Septum primum, B. Septum secundum, C. Endocardial cushions, D. Tricuspid valve orifice
A: Septum primum
Answer: A: Septum primum 
Explanation: Fossa oavlis represents the site of embryonic spectum primum hence from right atrium its seems to be developed from septum primum. BD CHAURASIA'S HUMAN ANATOMY.VOLUME 1. 6TH EDITION.PAGE NO 255