The given electrical network is equivalent to:

A) NOT gate
B) AND gate
C) OR gate
D) NOR gate

Hint: The logic gates form the unit of all the digital systems. The given electrical network represents the negative logic gates included in it. In order to calculate the required output of the given gates, get the output for the one by one and find for the last gate connected. Check it with the gates given in the option.

Complete step by step solution:
In the given electrical network, it represents the NOR gate, NOR gate and the NOT gate connected in series. The two NOR gates function opposite to that of the OR gate and the NOT provides the opposite result to the input. At first the first NOR gate is considered. In which the two inputs $A$ and $B$ are considered but gives the single output. This single output is fed into the other NOR gate. This gate takes only one output and also gives the one output which is opposite to the taken output. The output from the second NOR gate is taken into the NOT gate and gives the required output.
Let us construct the table of the given electrical network.

Hence the end of the NOT gate shows the output of the entire logic gate in the given electrical network. From the table, it is clear that the NOR gate alone for the given input, provides the same result to the whole logic gates in the electrical circuit. Hence the NOR gate is equivalent.

Thus the option (D) is correct.

Note: The logic gates like NAND and the NOR are called as the universal logic gates since they can perform the functions of the other logic gates like AND, OR and NOT. The single input NOR and the NOT gate perform the same functions to that of the NOT gate.