This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Surfaces and Grooves, Subject name: Anatomy
A structure marked with a red arrow is derived from which of the following ? 
Select and explain. 
A. Bulbous venosus, B. Septum primum, C. Endocardial cushion, D. Left venous valve
C: Endocardial cushion
Answer: C: Endocardial cushion 
Explanation: A structure marked with a red arrow is derived from endocardial cushion Structures derived from endocardial cushion are : Atrial septum Membranous pa of ventricular septum Atrioventricular canal, valves Aoo-pulmonary channels Any endocardial cushion defect = Cardiac malformation