We need to first define the parameters.
Radius:
A line segment extending from the center of a circle.
From the above definition, SU, SV and ST are radius.
Diameter:
A straight line passing from side to side through the centre of a circle.
From the above definition, TV is a diameter.
Chord:
The chord of a circle can be defined as the line segment joining any two points on the circumference of the circle.
From the above definition, TV and XW are chords of the circle.
Therfore, the statement that is NOT true is:
a.) Segment SU is a chord.
Because SU is a radius.