please answer the question in about 2 paragraphs

The yield-to-maturity (yield) of a bond is its return if you purchase it in the secondary market and hold it until it matures. So for example, if you bought a bond for $100 and its yield to maturity is 5%, then when the bond matures you get $105 back. Lets pretend we have two bonds. Bond A has a yield-to-maturity of 9% while Bond B has a yield-to-maturity of 2%. What are some reasons why Bond Bs yield is lower than Bond A? Hint: it has to do with types of risk.