Short Answer: AB Argument Take F to be the center. The line segment that IS a diameter or radius must either go through F (that would make the line a diameter) or to be a radius the segment mus end in F and touch the circumference once. See below.
The diameter must not only go through F, it must touch the circumference in two places. EFB is a diameter. So is AFC
The radius must have 1 endpoint at the center and one endpoint on the circumference. DF is a radius.
So what isn't? Answer: AB isn't. It neither goes through F nor is F one of the end points.
