The sensory registers a. are measures of retention b. retain past information c. control our attention span x d. receive sensory information from the external world

The sensory registers RECEIVED INFORMATION FROM THE EXTERNAL WORLD.
The sensory registers takes information from all the five sense organs and hold the information only for a few seconds, maximum of twenty seconds. Sensory register is the most intermediate form of memory which one have and it is the shortest form of memory.

It's either -limiting factors or -scarce resources but i'd go with my first answer since the food and water are abundant they really aren't scarce

Distillation.  distillation is the correct answer.