Jonathan Guyton researched maximum initial withdrawal rates and the variables that impact those rates. According to Guyton's studies, what percentage of equities in a retirement portfolio provides the best balance between risk, return and maximum initial withdrawal rate $($IWR$)?$

A$)$

$35\%$

B$)$

$40\%$

C$)$

$50\%$

D$)$

$65\%$