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
The investigation of choice for an ectopic pregnancy is: 
Select and explain. 
A. CT scan, B. Transvaginal USG, C. Serum HCG levels, D. MRI
B: Transvaginal USG
Answer: B: Transvaginal USG 
Explanation: B i.e., Transvaginal USG