a$.$ Now that you have the test results, you need to select one to invest in$.$ Please explain which one you choose and why.

$\backslash$table$[[$CPI$,0\mathrm{.}12,0\mathrm{.}08,0\mathrm{.}18,0\mathrm{.}12],[$D$1$ Retention Rate,$24\%,10\%,28\%,22\%$