Nitrogen and hydrogen 
N2 +3 H2 ---> 2NH3
hope that answers the question:)
        
                    
             
        
        
        
Answer: C. Black snakes will not prey on cane toads in areas where cane toads have been present for 40–60 years.
Explanation:
Cane toad secret a toxin called bufotoxin which is a defense mechanism against predators. These defense mechanism is capable of killing black snakes if they eat cane toads. Within a period of 40 to 60 years, the black snakes in these area will be aware of the presence of a toxin capable of killing them in cane toads and will not prey on them. This phenomenon is termed learned behavioral adaptation. 
 
        
             
        
        
        
HABITAT- marine environments that range from the shallow estuarine to the deep sea 
ADAPTATIONS
1. They are five- sided radial symmetry 
2. They are able to regenerate body parts , and some species of sea stars are even able to grow a new body from a severed arm. 
3. They have a water vascular system 
        
             
        
        
        
its actually not important  to have negative control  it needs to be positive control for the water to actually flow!