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
USG can detect gestation sac earliest at: 
Select and explain. 
A. 5-6 weeks of gestation, B. 7-8 weeks of gestation, C. 10 weeks of gestation, D. 12 weeks of gestation
A: 5-6 weeks of gestation
Answer: A: 5-6 weeks of gestation 
Explanation: A i.e. 5-6 weeks of gestation