The Graph Shows the Reciprocal of the Image Distance Plotted

The graph shows the reciprocal of the image distance plotted against the reciprocal of the object distance for a certain lens. From this graph it can be seen that this lens has a focal length of

A) 0.20 m.
B) 1.0 m.
C) 4.0 m.
D) 0.25 m.
E) -1.0 m.