Based on past data, the owner of a store believes that 80% of customers who walk in his store will make a purchase.Say, a random sample of 83 customers walks in his store and 69% of these made a purchase. What is the standard deviation of the sampling distribution of the sample proportion of customers who walk in and make a purchase in this store?

a, 0.00

b 0.04

c, -250.54

d, 0.05