This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Radiotherapy, Subject name: Radiology
Fetus is most radio sensitive at which week? 
Select and explain. 
A. 3 weeks, B. 8 weeks, C. 12 weeks, D. 15 weeks
A: 3 weeks
Answer: A: 3 weeks 
Explanation: ANSWER: (A) 3 weeksREF: Primer of radiobiology by Elizabeth Latorre Travis page 196The first trimester, particularly the first 6 weeks of development, appears to be the most radiosensitive in terms of both lethality and induction of congenital abnormalities in humansHence the answer is 3 weeks