Rods of equal length & equal cross - section are arranged as shown - The thermal conductivity of the rods are written correspondingly . The equivalent thermal conductivity of the system is -

Question

$(a)\;\large\frac{20}{3} K\qquad(b)\;\large\frac{10}{3} K\qquad(c)\;5K\qquad(d)\;None\;of\;these$