Answer:
B)
Explanation:
Natural selection describes how organisms change, and adaptation explains why. Charles Darwin, theory.
 
        
                    
             
        
        
        
Answer:
The nitrogenous bases guanine and adenine are A. purines.
Explanation:
Adenine and guanine are purines, whereas the other two bases in DNA (thymine and cytosine) are pyrimidines.  The main difference between purines and pyrimidines is the number of rings that the base has: purines have two rings while pyrimidines only have one ring.  
In addition, phosphate group and sugar group cannot be the answer to this question because these two elements in addition to a nitrogenous base makes up a nucleotide.
Hope this helps!
 
        
             
        
        
        
Answer:
The <u>nuclear  envelope</u> is composed of two concentric lipid bilayer membranes separated by an intermembrane space of about 20-40 nm. The outer membrane is continuous in many places with the rough endoplasmic reticulum. Like the rough ER the outer membrane of the nuclear envelope is dotted with ribosomes.