This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Medicine
A 21-year old male presents with exeional dyspnea, raised JVP and loud P2. ECG shows right axis detion. All of the following conditions are possible except' 
Select and explain. 
A. Atrial septal defect, B. Mitral stenosis, C. Ostium primum, D. Pulmonary thromboembolism
C: Ostium primum
Answer: C: Ostium primum 
Explanation: An ostium primum atrial septal defect (ASD) occurs when then atrial septum near the atrioventricular valves has a communication between the two atrium causing a left to right shunt. This rarely develops into Eisenmenger's syndrome if pulmonary hypeension develops reversing the direction of the shunt to right to left. Ref Davidson 23rd edition pg 453