This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Physics of Radiotherapy, Subject name: Radiology
1 grayis - 
Select and explain. 
A. I rad, B. 100 rad, C. 1 rem, D. 100 rem
B: 100 rad
Answer: B: 100 rad 
Explanation: Ans. is 'b' i.e., 100 rad o 100 Rad is equal to 1 gray or 1 rad is equal to 0[?]01 gray.Quantity measuredOld unitNew (SI) unit RadioactivityCurieBecquerel1 curie = 3[?]7 x 1010 Becquerel1 Becquerel = 2[?]7 x 10-11 curieRadiation exposureRoentgenColumb/cm Absorbed doseRadGray (Gy)100 rad = 1 Gray1 rad = 0[?]01 GrayDose equivalentRemSievert (Sv)100 Rem = 1 Sievert1 Rem = 0[?]01 Sievert