When estimating the cost of equity, which of the following serves as the most appropriate proxy for the riskfree asset as of July $12,2024?$

A$.$ Australian government bond maturing on $21$ Apr $2029$

B$.$ Australian government bond maturing on $21$ May $2034$

C$.$ Australian government bond maturing on $21$ Dec $2034$

D$.$ Australian government bond maturing on $21$ Jun $2054$