In a potentiometer null point for two resistance $R _ { 1 }$ and $R _ { 2 }$ is at 40 cm . If $16 \Omega$ is connected in parallel to $R _ { 2 }$ then null point is at 50 cm then $\mathrm { R } _ { 1 }$ and $\mathrm { R } _ { 2 }$ are respectively.
(A) $16 \Omega , 48 \Omega$
(B) $16 / 3 \Omega , 8 \Omega$
(C) $32 / 3 \Omega , 8 \Omega$
(D) $12 / 3 \Omega , 12 \Omega$