Answer:
the element oxygen , represented by the symbol o, is classified as a pure substance
 
        
             
        
        
        
<u><em>Naturally acquired active immunity:</em></u>  It happens when someone is exposed to a live disease and gets the disease. The person then becomes immune as a result of the first immune response. 
It's sort of like a fall and learn to get up for the body.
<em><u>Artificially acquired active immunity</u></em>:  It can be isert into the body by a vaccine so you won't get sick. That's why if you get a flu shot, you won't get the flu, if you get a chicken pox vaccine, you won't get the chicken pox. 
It's like you're body has a personal guide telling it where and where not to step in order to not fall.
 
        
             
        
        
        
C hope that helps have a great day :))))
        
             
        
        
        
Salt marshes are primarily influenced by the tidal flow.
        
                    
             
        
        
        
Answer:
the answers are a and d
Explanation:
Light, that is the main reason that we are able to see during the day because of the light
Heat if the sun is shining bright and youre outside you can feel the heat
have a great day :D