Thymine and cytosine are classified as "Pyrimidines" and have one ring of carbon and nitrogen atoms for each base.
        
             
        
        
        
A because I know it because I have the same test and it was right
        
                    
             
        
        
        
I think the correct answer would be A. The yolk sac becomes the placenta. It is membranous sac that is attached to the embryo. It provides all the nutrition and the blood cells needed by the embryo. It is also called the umbilical vesicle.
        
             
        
        
        
The answer to this one is D
        
                    
             
        
        
        
Answer:
The correct answer is B. A client who has increasing serum ammonia levels due to liver cirrhosis
Explanation:
Etiology is the study of origin or cause of any disease. Pathogenesis is the mechanism of causing disease by any pathogen. Pathogens use four-step to become pathogenic which are contact, colonization, invasion, and infection.  
In pathogenesis the symptoms of disease is observed not the cause so in option B increasing serum ammonia level is the symptom of liver cirrhosis which characterize pathogenesis rather than etiology and in other option, only cause of a medical condition is described so the correct answer is B.