Final answer:
The presence of complex ions, the formation of water, and gaseous products suggest the use of the half-reaction method for balancing redox reactions in aqueous solutions, as this method effectively deals with the involvement of water, hydronium ions, and hydroxide ions.
Step-by-step explanation:
The clue that might lead you to choose the half-reaction method of balancing equations rather than the oxidation-number-change method is the presence of complex ions (A), the formation of water (B), or gaseous products (C). Especially, when redox reactions occur in aqueous solutions there can be challenges in balancing the equations by the oxidation-number method, and the systematic approach of the half-reaction method is helpful. This method is advantageous for such reactions as it explicitly involves balancing water, hydronium ions, and hydroxide ions which frequently appear as reactants or products in aqueous media.