Black squirrels have a survival advantage over gray squirrels
 
        
             
        
        
        
Answer: lower atmospheric pressure 
Explanation:
During the inspiration process the diaphragm, and external intercostal muscles. The contraction of the diaphragm causes the increase in the size of the thoracic cavity this causes the contraction of the external intercostal muscles. As a result of this the ribs and the sternum get elevated.  
This causes the lungs to expand, and increasing the volume of the air passage. In this response the air pressure inside the lungs reduces below the air outside the body. Thus this facilitates the movement of the gases from a region of high pressure to low pressure, this way the air rushes into the lungs.
 
        
             
        
        
        
They would expect only about 5 hours of darkness.
        
             
        
        
        
Answer: Base pairs occur when nitrogenous bases make hydrogen bonds with each other. 
Explanation: Each base has a specific partner: guanine with cytosine, adenine with thymine (in DNA), The hydrogen bonds are weak allowing it to "unzip"