Fact 1: Biodiversity increases the productivity and stability of ecosystems.

Fact 2: Biodiversity is an incredibly powerful force that keeps species evolving.

Given the two facts above, answer the question "A force that keeps species what increases the productivity and stability of ecosystems?" with the following options: 
- evolving
 - protect them
 - recycling
 - ligt
 - animals
 - ferns
 - trees
 - heat


 

 evolving        