If $\mathrm{AB}$ is a double ordinate of the hyperbola $\frac{\mathrm{x}^{2}}{\mathrm{a}^{2}}-\frac{\mathrm{y}^{2}}{\mathrm{~b}^{2}}=1$ such that $\triangle \mathrm{OAB}$ is an equilateral triangle, where $\mathrm{O}$ is the centre of the hyperbola, then the eccentricity e of the hyperbola satisfies
(a) $1<\mathrm{e}<\frac{2}{\sqrt{3}}$
(b) $\mathrm{e}<\frac{1}{\sqrt{3}}$
(c) e $>\frac{2}{\sqrt{3}}$
(d) $\mathrm{e}=\frac{2}{\sqrt{3}}$