True, major events like a super volcano's or asteroid strikes can send tons of ash dust and debris into the stratosphere and cause global cooling. <span />
        
             
        
        
        
The correct answer is B) Treaties expanding International Trade
After the second world war, the world has gradually opened up to one another for trade and opportunities. 
We see that in the development of the World Trade Organization, as well as the NAFTA (North American Free Trade Agreement) between Canada, US, and Mexico and probably the most successful example in the European Economic Zone.
        
                    
             
        
        
        
 Answer:
I think that it is Eukaryotes 
Explanation:
 
        
                    
             
        
        
        
I'm not sure how exactly you wanted this question to be answered. You're either talking about the symmetry where animals would have two legs or two arms for example and thus producing a pair of each muscle on both sides of the body, or you're refering to the development of agonistic and antaonistic muscles where each of them served a different purpose; either extending or contracting.