Answer:
D. melting iron should be the answer because Iron wasn't used until the metal ages
 
        
             
        
        
        
Powers are shared between the state governments and the federal government. 
        
                    
             
        
        
        
Answer:
Narrow boats popular among tourists in Venice: Gondolas
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Explanation:
 
        
             
        
        
        
Answer:
D.  Christianity is the answer. 
Explanation:
 
        
                    
             
        
        
        
Answer:below Uchenna's absolute threshold
Explanation:An absolute threshold refers to the lowest level of stimulus that we can detect half the time.
It is used in neuroscience and during experiment in order to see what level of stimulus is an individual able to detect using their sense this involves detecting sound,taste,sight,smell and touch. For example for sound detection , a person hearing may vary with varying levels of volume, the lowest volume that one is able to hear 
half the times is called absolute threshold.