Which one of the following statements concerning Tellegen’s theorem is correct?

• A. It is useful in determining the effects in all parts of a linear four-terminal network
• B. It is applicable for any lumped network having elements which are linear or nonlinear, active or passive, time-varying or time-invariant, and may contain independent or dependent sources.
• C. It can be applied to a branch, which is not coupled to other branches in a network
• D. It states that the sum of powers taken by all elements of a circuit within constraints imposed by KCL and KVL is non-zero.