Penny-wenny

Duration can be understood as the percent change in price due to a change in rates. The question states that there is going to be a decline in interest rates..thus what would be the best portfolio to choose from...the one that would have the highest duration or interest rate risk.

Duration is greatest for bonds that have:

longer maturities,
lower coupons,
lower initial yields.

Based on that definition, and those guidelines..C would have the greatest increase in value.