JAMB Physics 1981 Question 44

In a light experiment with a convex lens a student plotted a graph, shown above (Fig. 6), of the reciprocal of object distance (1/U) against the reciprocal of the image distance (1/V). The focal length of the lens is given by

1. A.slope of the line PQ
2. B.reciprocal of either OP or OQ
3. C.length OP or OQ
4. D.area under the graph
5. E.ratio OP/OQ.