spot rates for years $1$ to $2$ are $9\%$ and $10\%.$ A three$-$year bond with $6\%$ annual payment coupon rate has a yield to maturity of $8\mathrm{.}50\%.$ Then the three$-$year spot rate is A$-9\mathrm{.}00\%.$ B$-8\mathrm{.}72\%$ C$-8\mathrm{.}43\%$