The right answer is C. I think, a. and d. are obviously not serious. B is not true, because Ag and Au are in the same group in the periodic table and therefore have the same number of electrons in the last level. So, they form ions with the same charge. C is true beacause Ag and Au have different numbers in the periodic table and different amount of protons and neutrons in their nucleuses. 
        
             
        
        
        
Every 3 days the stomach starts a new lining
 
        
             
        
        
        
Answer: Selective breeding
Explanation:
Selective breeding or artificial breeding is a process that allows humans to select parents in plants and animals that have desirable traits. Such parents are bred to produce offspring that have desirable traits from both parents. Humans have bred many species of plants and animals to improve the quality of plant and animal yields in terms of crops, milk, meat, eggs, and other derivatives. 
 
        
             
        
        
        
I believe <span>Protease enzymes are what are used to break proteins into amino acids.</span>
        
             
        
        
        
Its Unipotent !! C!! the word itself describes if you try to understand!!