Compute the holding period return $($HPR$)$ for a $4\%$ U$.$S$.$ Treasury bill bought at a discount of $$971$ exactly six months ago that matures today.

a$.4\mathrm{.}90\%$

b$.10\mathrm{.}09\%$

c$.5\mathrm{.}05\%$

d$.7\mathrm{.}11\%$