\textbf{123.} A hyperbola with semi-axes of lengths $9$ and $16$ units is inscribed in a circle with circumference $16$ units. What is the shortest distance from the vertices of the hyperbola to one vertex of the smaller base of the hyperbola?
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(1) $\dfrac{3}{2}$ \hfill (2) $\sqrt{3}$ \hfill (3) $2$ \hfill (4) $\dfrac{5}{2}$
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