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Q)

If $a=\cos\alpha+i \sin\alpha$, $b=\cos\beta+i \sin\beta$, $c=\cos\gamma+i\sin\gamma$ and $\large\frac{b}{c}+\frac{c}{a}+\frac{a}{b}$ = 1, then $\cos(\beta-\gamma)+\cos(\gamma-\alpha)+\cos(\alpha-\beta)$ = ?

$\begin{array}{1 1}(A) \large\frac{3}{2} \\ (B) \large\frac {-3}{2} \\ (C) 0 \\(D) 1 \end{array}$