connect First 4 Lamps(L1 , L2 , L3 , L4) to extension 1 and take power from Extension 2 . In Extension 2 we can connect only 3 lamps because out of 4 one port is busy to supply power to extension 1.
Similarly, For other extensions we can connect only 3 lamps because one port is busy to supply power to other extension.
Connect Last Extension (Ex 19) to Electric outlet.
We can connect 4 Lamps to first extension
Number of Extension required for Remaining 54 lamps = $\frac{54}{3}$=18 Extension
Total Extension required to connect all 58 Lamps = 18+ 1 =19
Hence,Option(D)19 is the correct choice.