When interest rates decline (lets say from 5% to 2% on long-term US Treasury bonds), youd want to own a non-callable US Treasury bond with a duration of 10 over a US mortgage bond with a duration of 5 because:

A Mortgage bonds have less reinvestment risk

B Mortgage bonds rise less than Treasury bonds since they are callable bonds

C Duration for the 10-year Treasury bond indicates that it is less sensitive to changes in interest rates than the 5-year duration mortgage bond

D Lower rates could be a sign of a recession, and during a recession one would prefer mortgage bonds as they have more liquidity than Treasury bonds