A straight line drawn perpendicular to the axis and terminated at both end of the curve is a _________________ of the parabola.

$\begin{array}{1 1}(a)\;\text{double ordinate}\\(b)\;\text{coordinates of vertex}\\(c)\;\text{focus}\\(d)\;\text{none of these}\end{array}$

A straight line drawn perpendicular to the axis and terminated at both end of the curve is a double ordinate of the parabola.
Hence (a) is the correct answer.