The correct answer is B.
OBJ-4.1: The annual rate of occurrence is 0.05 since one incident occurs every 20 years (1/20 is 0.05). The annual rate of occurrence (ARO) is the number of times in a year that a single event occurs. If the number of times an event occurs is counted over multiple years, then the number is divided by the number of years to calculate the ARO. If the number of times is counted monthly, then it is multiplied by 12 to annualize it. For example, if the number of occurrences was 3 times per month, then the ARO would be 36 times per year (3 occurrences x 12 months in a year).