Answer:
a) tangent
b) radius
c) diameter
d) chord
Explanation:
You want the vocabulary words associated with various segments in and around a circle.
Tangent
A tangent is a line or segment that is external to the circle and intersects it at one point. A tangent is always perpendicular to a radius. (Segment a is a tangent.)
Radius
A radius of a circle is a line segment between the center and a point on the circle. (Segment b is a radius.)
Chord
A chord is a line segment internal to the circle that joins two points on the circle. (Segment d is a chord.)
Diameter
A diameter of a circle is a chord that contains the center of the circle. (Segment c is a diameter, and also a chord. The more specific descriptor is "diameter.")