The Method Used to Conclusively Identify the Best Place to Drill

The method used to conclusively identify the best place to drill a well is to:

A) employ the services of dowsers, because they have been proven completely reliable.
B) survey an area's vegetation because certain plant species indicate specific depths of the water table.
C) locate sources of surface water because such sources intersect the water table.
D) drill test wells, because they show the depth of the water table at particular places.