A stock has yielded returns of $-9$ percent, $16$ percent, $12$ percent, and $6$ percent over the past four years, respectively. What is the standard deviation of these returns?O A$.10\mathrm{.}97\%.11\mathrm{.}98\%$ C$.12\mathrm{.}35\%$ D$.15\mathrm{.}52\%$E$.9\mathrm{.}60\%$