Answer:
A circle is named by its center.  The center of the given circle is A, therefore:
<u>Name of the circle:</u>  A
<u />
The radius is any line segment from the center of the circle to the perimeter.
<u>Name 4 radii:</u>  
A major arc is an arc whose measure is greater than 180°.
When naming a major arc, the first point and last point are the endpoints, and we also need include the name of any point between those two endpoints.
<u>2 major arcs:</u>   <u />
<u />
<u />
A semi-circle is half a circle with an arc that measures 180°.
Its endpoints lie on the diameter of the circle.  We need three points to name a semicircle (the endpoints and a point between the endpoints).
<u>A semi-circle:</u>  CEF
A minor arc is an arc whose measure is less than 180°.
<u>3 minor arcs:</u>  
A central angle has its vertex at the center of the circle, and is formed by 2 radii.  When naming the central angle, the middle letter is the center of the circle.
<u>3 central angles:</u>   
 
The diameter is the widest part of the circle.  It is a straight line segment that passes through the center of the circle.
<u>A diameter:</u>  CF
Congruent angles are angles with the same measure.
On the diagram, the same angle measures are indicated by the addition of the same number of dashes on the angle sign.
<u>Congruent angles:</u>  
Adjacent arcs are arcs that have one point in common.
<u>Adjacent arcs:</u>   and
 and  (they share point B)
  (they share point B)