Please show formulas and calculations

Question $2(0\mathrm{.}5$ points$)$

You have developed the following data on three stocks:

If you are a risk minimizer, you should 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.

C; A

A; A

C; B

A; B

$B$;$A$

Please show formulas and calculations