The correct answer is (A) elevated dividing point; a ridge of land that separates two different drainage areas; the crest line that divides the land drained by two different rivers; water parting; divide; the catchment area of a river system.

Watershed comes from Old English waeter (water) and sceadu (separation).

Examples of use:

• The line of watershed for several rivers lies high up in that mountain range.
• We hope that the treaty will become `one of history's great watersheds.