The Bank of Fast Loans uses the following rating scheme to classify the riskiness of its customers. Risk Class Prime High grade Upper medium grade Risk Premium (%) .05 1.0 1.5 Lower medium grade 2.0 Speculative: Non-investment grade 4.0 Speculative: Highly 6.0 Substantial risks 9.0 Extremely speculative 12.0 The bank's pure rate of interest is 2% and the inflation premium is 3.5%. The bank offers an annual rate of 6.63% to a customer. What is the risk class of this customer? A. Speculative: Non-investment grade B. Lower medium grade C. High grade D. Substantial risks E. Upper medium grade F. Speculative: Highly