Answer:
I think A. is the right answer. 
Explanation:
I searched up on how to determine population size and here here are some things I found. ¨The number of individuals in a specific area¨, ¨The most obvious way to determine the size of a population is to count, one by one.¨, but one thing I´m kinda sure is right is this one. It´s determining population size.  ¨Some methods of determining the size of population are direct and indirect observations, sampling, and mark-and-recapture studies¨ But just see for yourself.
 
        
             
        
        
        
Answer:
Carbon dioxide, water, and energy.
Explanation:
I hope that this helps!
 
        
             
        
        
        
Answer:
C.
Explanation:
"Cellular respiration, the process by which organisms combine oxygen with foodstuff molecules, diverting the chemical energy in these substances into life-sustaining activities and discarding, as waste products, carbon dioxide and water."
 
        
                    
             
        
        
        
Answer:
It is very possible for a plant to grow on mars, but you would need better soil, because mars' soil is filled with perchlorate salt which is toxic to plants. You would also need to conceal the plant, because the temperatures on mars are usually freezing. But yes, you could have a cactus on mars, it would just be very difficult to sustain.
Explanation: