DNA is unzipped by helicase at the origin of replication. There are several origins of replications in eukaryotic DNA replication, while only one in prokaryotic replication.
        
             
        
        
        
Pretty sure it would be A it makes the most sense
        
                    
             
        
        
        
Erosion is brought about by the forces of nature or human activity: water, wind, earthquakes, mining, quarrying, etc. In the desert, there is very little water that can cause weathering or erosion, so the most probable answer is wind or maybe even animal activity.
        
                    
             
        
        
        
Cell
Tissue
Organ
Organ system
Organism
Brain, spinal cord, nerves
The brain controls thought, behavior, emotion, memory, and basic life functions. The brain is also the origin of control over body movement. The spinal cord connects the peripheral nervous system (PNS) to the brain; nerve impulses reaching the spinal cord through sensory neurons are transmitted up into the brain. Nerves primarily involve control and coordination of all parts of the body. 
The nervous system interacts with every other organ system. For example the hypothalamus in the brain controls the pituitary gland and tells it when to produce hormones, this shows that the nervous system interacts with the endocrine system. 
Hope this helps :)
        
             
        
        
        
Chicken with feather or depending on what you cross breed it with