A client requires a lump sum of money in $8\mathrm{.}5$ years. Using the following bonds, which bond portfolio effectively immunizes the client from changes in interest rates?

Bond

Weights

a$.$

b$.$

c$.$

d$.$

Ifond $A$

$20$

$20$

$\mathrm{.}00$

$40$

Bond B

$80$

$\mathrm{.}50$

$60$

$00$

Bond C

$00$

$30$

$40$

$60$