This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
Which is going to best declare the case as that of interatrial septal defect with other cardiac abnormalities – 
Select and explain. 
A. Elevated pressurein left atrium, B. Elevated pressure in right atrium, C. Elevated PO2 in pulmonary artery, D. Systolic murmur
B: Elevated pressure in right atrium
Answer: B: Elevated pressure in right atrium 
Explanation: None