The first sentence. When you're talking about more than one elf it is elves not elfs. 
        
                    
             
        
        
        
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Because unlike other scientists at his time, he believed the Earth was the center of the universe.  The opposite of the geocentric model is the heliocentric, where the Sun is the center of the universe (correct model).
 
        
             
        
        
        
how the quantity that a person will demand varies depending on the price of a good or service.
 
        
                    
             
        
        
        
Answer:
Explanation:
Attitudes to World War 1 (WW1) known as 'The Great War' changed throughout the duration of the conflict. At the outbreak of war the general attitude to the war was positive; the British public had feelings of euphoria. ... British people had not experienced anything on this scale for over a century.The First World War differ from previous wars because its reliance on advanced industrial technology and the elaborate economic and political organization of belligerent nations. The first widespread use of machine guns, air power, submarine operations, poison gas and armored vehicles. You just studied 5 terms!