Given the project data below, what is the standard deviation of durations for path $A,B,C?$

$\backslash$table$[[$Task$,$Predecessors,$\backslash$table$[[$Best$],[$Case$]],\backslash$table$[[$Most$],[$Likely Case$]],\backslash$table$[[$Worst$],[$Case$]]],[$A$,$None,$2,4,6],[$B$,$A$,1,4,5],[$C$,$B$,\mathrm{.}5,1,6]]$

A$.1\mathrm{.}4$

B$.2\mathrm{.}3$

C$.1\mathrm{.}7$

D$.$ None of the choices is correct