You are presented with the question "What grow in width and length.?" and the following answer choices: 
- crocodiles
 - sedimentary rocks
 - vegetation
 - remains of prehistoric life
 - swamp vegetation
 - shrub beds
 - underground systems
 - loose dirt

Now knowing that roots grow in length and width from primary and secondary meristem and kids see the underground root systems of trees and then an aerial view of plants in the city, choose the best answer.


 

       underground systems  