The communities plus abiotic and biotic surroundings is called an ecosystem 
        
             
        
        
        
Perception of pitch and sound intensity is the cocklear
        
             
        
        
        
A replication bubble forms as the DNA unwinds.
Option C  
<u>Explanation</u>:  
Replication bubble is the space where the strands of double helical DNA structure are separated with the help of DNA helicase. The strands of the double helical DNA are still in the helix form on the both end of the unwinded DNA stand which gives this region an appearance of a bubble. 
DNA unwinding is the first step in replication or transcription of the DNA molecule. DNA helicase separates the two types of "DNA" that are connected by hydrogen bonds with the help of ATP hydrolysis.  
 
        
             
        
        
        
Archaeologist
hope it is correct