Which of the following discontinuities is easiest to detect with an electromagnetic test? (Assume that the area of the discontinuity is equal in all four choices listed.)

A subsurface crack which lies parallel to the direction of the eddy current.

A discontinuity located in the center of a 51 mm (2 in.) diameter bar.

A radial crack that extends to the outer surface of a 51 mm (2 in.) diameter bar.

A subsurface radial crack located at a depth of 13 mm (0.5 in.) in a 51 mm (2 in.) diameter bar.