Portfolio diversification allows investors to reduce risk by investing in a variety of assets. It is especially effective when the correlation between the assets is low. Consider the accompanying table, which shows a portion of monthly data on stock returns of five companies in from October $2015$ to September $2017.$

$\backslash$table$[[$Date$,$RET$\_$MONRET$\_$FB$,$RET$\_$TSLARET$\_$C$,$RET$\_$CWST$,,],[\frac{10}{1}\frac{?}{15},9\mathrm{.}233659,13\mathrm{.}42603,-16\mathrm{.}6948,7\mathrm{.}175966,4\mathrm{.}655172],[\frac{11}{1}\frac{?}{15},2\mathrm{.}710792,2\mathrm{.}226142,11\mathrm{.}27435,1\mathrm{.}730303,11\mathrm{.}69687],[\frac{12}{1}\frac{?}{15},3\mathrm{.}530901,0\mathrm{.}402922,4\mathrm{.}234344,-4\mathrm{.}32612,-11\mathrm{.}7994]]$

Click to download full dataset Excel file.

Question $19$: Compute the correlation coefficients between all pairs of stock returns. Suppose an investor already has a stake in Citigroup $($C$)$ and would like to add another asset to her portfolio. Which of the remaining three assets will give her the maximum benefit of diversification? $($Hint: Find the asset with the lowest correlation with Citigroup $($C$)).$