c
Given lines will be concurrent if
$\left|\begin{array}{lll}{1} & {2 a} & {a} \\ {1} & {3 b} & {b} \\ {1} & {4 c} & {c}\end{array}\right|=0 \Rightarrow-b c+2 a c-a b=0$
$\Rightarrow \mathrm{b}=\frac{2 \mathrm{ac}}{\mathrm{a}+\mathrm{c}} \Rightarrow \mathrm{a}, \mathrm{b}, \mathrm{c}$ are in $\mathrm{H.} \mathrm{P.}$