As a straight line perpendicular to the ground line in both projections.
As a straight line parallel to the ground line in both projections.
Like a straight line in the horizontal plane and an oblique straight line in the vertical plane.
As a straight line in the horizontal plane and a straight line perpendicular to the ground line in the vertical plane.Correct
A horizontal projecting plane is represented as a line in the horizontal plane (its horizontal trace) and as a line perpendicular to the ground line in the vertical plane.