Answer: The answer is the directrix.
Step-by-step explanation: We are asked that the vertex, which is the extreme point of a parabola lies between focus and which point or line segment.
Attached herewith, a picture of a standard parabola. We can easily see that the focus and the directrix lies on two opposite sides of the vertex and the vertex is in the middle of the focus and the directrix.
So, the vertex lies in the halfway of the focus and the directrix.
Thus, the answer is the directrix.
