Let $\alpha , \beta , \gamma$ be complex numbers which are the vertices of an equilateral triangle. Then, we must have:\\
(A) $\alpha + \beta + \gamma = 0$\\
(B) $\alpha ^ { 2 } + \beta ^ { 2 } + \gamma ^ { 2 } = 0$\\
(C) $\alpha ^ { 2 } + \beta ^ { 2 } + \gamma ^ { 2 } + \alpha \beta + \beta \gamma + \gamma \alpha = 0$\\
(D) $( \alpha - \beta ) ^ { 2 } + ( \beta - \gamma ) ^ { 2 } + ( \gamma - \alpha ) ^ { 2 } = 0$