C. All cells arise form previously existing cells. This is because the scraped knee's cells would be replaced by the exact same ones that were removed. Kind of like "Out with the old and in with the new... yet the exact same..!" 
Hope this helps!
        
                    
             
        
        
        
No all rock dont have to go through a complete life cycle......i mean some could it but  it dont have to be in any exact order ..... so your answer would be false
        
             
        
        
        
Answer:
it is the change in one or more genes
 
        
                    
             
        
        
        
Answer:
Explanation:
Each chromosome represents a twin.like pairs of socks.
This is an analogous problem: you have 2 pairs of socks, one white, one black. Each of the sock is tailored to a specic foot, right or left. How many different ways can the socks be mixed and matched , one for each foot?
 Here are the possibilities : left = black, right = black is one such match. Left = white, right = black is another.
so also we will have 23 chromosome pairs