First of all, we can clearly tell that a straightedge was used to create CD but that doesn't prove anything so we can eliminate the second and fourth options. Upon measuring the lengths of AC and CB, we see that they are equal so the answer is Yes; the compass was kept at the same width to create the arcs for points C and D. The reason why this is so important is because we know that AC = CB = BD = DA because the compass width is the same, so therefore, ACBD is a rhombus based on the definition of a rhombus. We know that the diagonals of a rhombus bisect each other and since CD and AB are diagonals, we know that CD bisects AB.
