a$.$ What is the duration of a zero$-$coupon bond that has nine years to maturity?

b$.$ What is the duration if the maturity increases to $11$ years?

c$.$ What is the duration if the maturity increases to $13$ years?

$\backslash$table$[[,],[$a$.,$Duration of the bond,,years$],[$b$.,$Duration of the bond,,years$],[$c$.,$Duration of the bond,,years$]]$