An important scientist at the time, besides, those who were mentioned was Copernicus - A.
Spartacus was just a slave general in the Roman republic. 
Rousseau was a philosopher.
Plato was a philosopher as well.
The correct answer for that reason is Copernicus, he was an astronomer and a major figure at the time. 
        
                    
             
        
        
        
Answer:
The answer is B) Crusaders returned to Europe with new ideas
 
        
                    
             
        
        
        
Folowing World War II, The world's leaders promoted peace and reduced poverty by starting and participating in the United Nations. United Nations promoted  cooperation between nations, instead of aggression. It is an intergovernmental organization created to keep international peace and security, develop friendly relations among nations, achieve international co-operation and be a centre for harmonizing the actions of nations.
 
        
                    
             
        
        
        
Answer: if you are interested in the formula you can check the video at the link below - it contains instructions about how to calculate the age of an object based on the carbon-14 atoms.. and it should be pretty self explanatory!
Explanation: