Fact 1: Some arthropods have special excretory structures.

Fact 2: Terrestrial arthropods have an excretory system that conserves water and eliminates waste.

Given the two facts above, answer the question "What is the name of something some animals use to conserve water and elminate waste?" with the following options: 
- it keeps an organism warm
 - food and shelter
 - Exfoliation
 - an area swollen with pus
 - swamp vegetation
 - excretory structures
 - reusing materials
 - colder and wetter


 

      excretory structures   