The correct answer is D. All of the above.
The circulating current method, Thevenin’s theorem, and superposition of currents are all methods that can be used to solve network problems in interconnected systems.
The circulating current method is a technique for analyzing networks with multiple loops. It involves calculating the currents that circulate around each loop in the network. Thevenin’s theorem is a method for simplifying a network by replacing one or more of its components with an equivalent circuit. Superposition of currents is a method for analyzing networks with multiple sources of current. It involves calculating the current through each branch of the network due to each source of current individually, and then adding the individual currents together to find the total current.
Each of these methods has its own advantages and disadvantages. The circulating current method is relatively simple to use, but it can be difficult to apply to networks with a large number of loops. Thevenin’s theorem is more general than the circulating current method, but it can be more difficult to apply. Superposition of currents is the most general method, but it can be the most difficult to apply.
The choice of which method to use depends on the specific network that is being analyzed. In some cases, it may be necessary to use a combination of methods.