<u>Answer:</u>
Eradicating smallpox was successful because of many reasons.
<u>Explanation:</u>
Smallpox was regularly found in an area or we can say it was prevalent in some places. So, mortality rates were high. It was caused by variola virus and affected mainly humans. So, it was essential that such vaccine is developed which can successfully immune people from this disease.  
Smallpox vaccine then started spreading across "Europe and North America" and then gradually it spread all over the world and successfully eradicated smallpox by 1980. Other diseases that have been controlled by vaccines are “diphtheria, bacterial influenza, measles, mumps, rubella, and tetanus”.
 
        
             
        
        
        
Benvolio is talking about Rosaline.
Explanation: 
Romeo has not yet met Juliet at the Capulet party and he does not know about Juliet at this point in the play. The only woman that he loves is Rosaline but that changes when he sees Juliet.