Spring Corporation's bonds have a maturity of 30 years with a $12,250 face value and a 5.5% semi-annual coupon. They are callable in 15 years at $11,750 and currently sell at a price of $12,000. a) What are their nominal annual yield to maturity and their annual yield to call? b) What return should investors expect to earn on these bonds? c) What is the most reliable market indicator for bonds ratings or yield spreads? Please choose one.