This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
The 10days rule is related to 
Select and explain. 
A. Sewage disposal, B. Air quality, C. Water quality, D. Radiation protection in pregnancy
D: Radiation protection in pregnancy
Answer: D: Radiation protection in pregnancy 
Explanation: The "10-day rule" recommended that, in women of child-bearing potential, non-urgent x-ray examinations that entailed pelvic irradiation should be restricted to the first 10 days of the menstrual cycle. Its rationale was to avoid irradiating a fetus before the mother realised that she was pregnant. In 1984, however, the International Commission on Radiological Protection repoed that there was little, if any, the risk of damaging the fetus during the first two weeks of gestation--that is before the first period was missed.