You are considering investing in one of the these three stocks:

$\backslash$table$[[$Stock$,$Standard Deviation,Beta$],[$A$,12\%,-0\mathrm{.}21],[$B$,30\%,0\mathrm{.}78],[$C$,9\%,1\mathrm{.}23]]$

If you are a strict risk minimizer, you would choose Stock $\_$ if it is to be held in isolation, and Stock if it is to be held as part of a well$-$diversified portfolio.