Its not exactly a well worded question but Barron assumes that you assumes the O is the centere and OA and OB are radii.

Not the best thing to tell GRE students as GRE sometime traps students by wording the questions differently from the images.


While we are at it: Solution to the problem.

We have an isosceles triangle OAB. Now when the center angle X is cloase to 180 degrees. The perimeter of the triangle is almost 20.

As \(OA =5\) and \(OB = 5\) and \(AB = \approx 10\)


Now when the center angle X is close to 90 degrees. The perimeter of the triangle is almost 17.07.

As \(OA =5\) and \(OB = 5\) and \(AB = \approx 5\sqrt{2}\) As triangle OAB is right isosceles triangle.

Thus we can say: as \(90<x<180\) or \(7.07 < AB < 10\) so \(17.07 < Perimeter < 20\)

Hence A is the correct option.