Use the information for the question(s) below. 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 firm there is a 70% probability that the firm will have a 20% return and a 30% 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. 5.10%. B. 15.0%. C. 5.25%. D. 23.0%.