Demand in each period follows the same normal distribution (i.e., there is one demand distribution that represents demand in any single period). Assuming demand is independent across periods, which of the following statements about the standard deviation of demand over five periods is true? 

a. It equals the standard deviation of demand over one period. 

b. It is greater than the standard deviation of demand over one period but less than five times the standard deviation of demand over one period. 

c. It equals five times the standard deviation of demand over one period. 

d. It is even more than five times the standard deviation of demand over one period.