A firm's bonds were selling at par value but have recently gone up in value and now sell at a significant premium? Which of the following could cause this?

• The firm recently announced it would be issuing much more debt in order to buy back common stock.
• Investors perceive that the firm's risk profile has decreased significantly.
• Investors perceive that the firm's risk profile has increased significantly.
• The general level of interest rates in the economy have gone up significantly.