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: Radiology
Best for unruptured ectopic pregnancy is: 
Select and explain. 
A. Per abdominal US, B. HCG, C. Trans vaginal US, D. Amniocentesis
C: Trans vaginal US
Answer: C: Trans vaginal US 
Explanation: C i.e. Tranvaginal US