Fact 1: An animal requires energy to move.

Fact 2: And as they move or run, their legs barely move.

Given the two facts above, answer the question "What requires energy?" with the following options: 
- trees staying in place
 - animals with backbones
 - Veins and arteries.
 - statues not moving
 - some invertebrates
 - rocks remaining still
 - power stations
 - animals running


 

        animals running 