Correct Option: C

The given network:

Let R = R_L.
The value of R required for maximum power transfer in network is equivalent to net resistance as seen from the open load terminal (i.e. Thevenin’s resistance, R_th)

From above figure,
R_th = [5 || 20] + 4Ω = 4Ω + 4Ω = 8Ω
Hence alternative (C) is the correct choice