Answer:             Water pollution also affects the ecosystem – it can cause a phenomenon called eutrophication. This can cause fish and other aquatic organisms to die. Toxic elements dissolved in water can make their way to humans through fish or other aquatic organisms.
https://byjus.com/biology/effects-of-water-pollution/
Explanation:
 
        
                    
             
        
        
        
Answer:
Option D, A subject is observed both before and after two exposures to the treatment.
Explanation:
In A-B-A-B design the alphabets have following meaning
a)	First A – It is the baseline value or the value measured before treatment
b)	First B – It is the treatment measurement
c)	Second A  - It is the withdrawal of treatment  
d)	Second B – It is the reintroduction of treatment  
The second A is known as the reversal phase in which the intervention is withdrawn to see if the target behavior returns to the baseline behaviour
Thus , there are two measurements involved one before the intervention and second after the intervention
Option D is correct
 
        
             
        
        
        
Answer:
No, coal is not a mineral because coal is made of dead plants 
Explanation:
Coal is formed when dead plant matter decays. Minerals are chemical compounds. 
Minerals are not formed from plants or animals 
 
        
                    
             
        
        
        
Answer:
B
Explanation:
If the traits are favorable this means nature would select it.
 
        
             
        
        
        
Answer:
Answer is A.
Explanation:
H2O, meaning 2 hydrogen and 1 oxygen. This is the recipe for water basically.