Which of the Half-Reactions Below Would Be Complementary and Balance

Multiple Choice

Which of the half-reactions below would be complementary and balance the following half-reaction? Zn⁺² → Zn

A) Cu → Cu⁺²
B) K⁺ → K
C) 2 Cu → 2 Cu⁺²
D) 2 K⁺ → 2 K
E) Cl₂ → 2 Cl^-