A $20-$year Amazon bond pays $9\%$ interest annually on a $ $1,000$ par value. If the bond currently sells for $ $945,$ what is the bond's yield to maturity?

a$.9\mathrm{.}63\%$

b$.9\mathrm{.}00\%$

c$.10\mathrm{.}63\%$

d$.20\%$