A network consisting of a finite number of linear resistor (R), inductor (L), and capacitor (C) elements, connected all in series or all in parallel, $$\sum\limits_{k = 1}^3 {{a_k}\cos \left( {k{\omega _0}t} \right),} $$    where a_k ≠ 0, ω₀ ≠ 0. The source has nonzero impedance. Which one of the following is a possible form of the output measured across a resistor in the network?

A. $$\sum\limits_{k = 1}^3 {{b_k}\cos \left( {k{\omega _0}t + {\phi _k}} \right),} {\text{ where }}{b_k} \ne {a_k},\,\forall k$$

B. $$\sum\limits_{k = 1}^3 {{b_k}\cos \left( {k{\omega _0}t + {\phi _k}} \right),} {\text{ where }}{b_k} \ne 0,\,\forall k$$

C. $$\sum\limits_{k = 1}^3 {{a_k}\cos \left( {k{\omega _0}t + {\phi _k}} \right)} $$

D. $$\sum\limits_{k = 1}^2 {{a_k}\cos \left( {k{\omega _0}t + {\phi _k}} \right)} $$

Answer: Option A