Answer:
The correct option is 4. Points S and T are the vertices of the ellipse.
Explanation:
The end points of the major axis are called vertices of the ellipse and the end points of minor axis are called co-vertices.
The standard form of an ellipse is

If a>b, then vertices are (± a,0) and co-vertices are (0, ± b).
If a<b, then vertices are (0, ± b) and co-vertices are (± a,0).
From the given figure it is clear that major axis is ST and minor axis is QR. So, points S and T are vertices and points Q and R are co-vertices of the ellipse.
Since the end points of the major axis are called vertices of the ellipse, therefore the point S and T are the vertices of the ellipse.