Consider an economy with two types of firms, S and I. S firms always move together, but I firms move independently of each other. For both types of firms there is a 40% probability that the firm will have a 20% return and a 60% probability that the firm will have a -30% return. The standard deviation for the return on a portfolio of 20 type I firms is closest to: A. 12.25% B. -10% C. 24.49% OD. 5.48%