In a vernier callipers one main scale division is x cm and n division of vernier scale coincides with $(n-1) $ divisions of main scale least in cm is

Question

$\begin{array}{1 1} (a) \;\bigg(\large\frac{n-1}{n}\bigg)^n \\ (b) \;\large\frac{nx}{(n-1)} \\ (c) \;\large\frac{x}{n} \\ (d) \;\large\frac{x}{x-1} \end{array} $