Conceptually, a drainage basin terminates at the that is a line of separation between runoff that descends in the direction of the drainage basin and runoff that goes toward an adjacent basin.

drainage divide.

Explanation:

A drainage basin is a type of basin in which rain water collects on an area of land and later drains off into other water bodies such as river, bay, etc. A drain basin consists of a snowmelt, surface runoff, groundwater, etc. Drainage basin always connects with other basin at lower altitude and in a hierarchical pattern.

Drainage basin is also called impluvium, catchment basin, river basin, drainage area.

the answer is the last option or letter d)