Take the midpoint d of AB and connect OD and CD.

In the triangle OAB, the angle AOB=90 degrees, AD=DB, OD= 1/2AB=2.

In the triangle ACD, the angle CAB=90 degrees, AC=2, AD= 1/2AB=2, and CD=2√2.

According to the shortest line segment between two points, OD+CD >；; =OC (when o, c and d are in a straight line, the equal sign holds)

Therefore, oc