The quadilateral can be formed as,
As both the circle have same radius AB, hence the radius of the circle with center A have,
AC=AB=AD.....(1)
Also for circle with center B,
BD=BA=BC....(2)
From (1) and (2),
AB=BC=CD=DA.
Thus,all four sides of the quadilateral are equal.
But triangle ABC is an eqilateral triangle from equation (1) and (2), hence angle C will be 60 degrees.
A quadilateral with all four sides equal and one angle equals to 60 degrees must be rhombus.
Thus, option (a) is correct.
