Answer:
The fourth plant that receives pure water is the control group. 
Explanation:
The election of a control group is essential in an experiment. Its principal purpose is to allow the discrimination of the results obtained by the treatment in the study, in this case, <em>the different concentrations of salty water that each plant receives</em>. The control group provides a reference point. It must be selected from the same population of the treatment groups. Both groups must be similar in every variable that might influence the results, <u>except for the study treatment.</u>
 
        
             
        
        
        
Answer: Coral reefs are important to the ecosystem because they are the pillars on which marine and coastal ecosystems are built. They keep plants, fish, and animals fed. They clean up our water and protect our coasts.
Explanation: Hope it helps :)
 
        
             
        
        
        
D.
Both organisms have the same genus in their scientific name meaning they are members of the same family and order.