Answer: option C) cowpox and smallpox are caused by the same virus
Explanation:
Cowpox is a skin disease that affects cattle. It is caused by an Orthopoxvirus, with lesions occurring principally on the udder and teats of the animals. 
Human infection may occur from touching infected cows, and thus giving immunity to smallpox (an acute infection caused by the same poxyvirus, in HUMANS) 
So, Jenner's successful use was because cowpox and smallpox are caused by the same virus
 
        
             
        
        
        
An estuary is an area where a freshwater river or stream meets the ocean. In estuaries, The salty ocean mixes with a fresh water river, resulting in brackish water. Brackish water is someone salty, but not as salty as the ocean. An estuary may also be called a bay, lagoon, sound, or slough.
 
        
             
        
        
        
Carbon dioxide is emitted as a by-product of clinker production an intermediate product in cement manufacture, in which calcium carbonate (CaCO3) is calcinated and converted to lime (CaO), the primary component of cement. CO2 is also emitted during cement production by fossil fuel combustion.
        
                    
             
        
        
        
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