Answer: A sum
Step-by-step explanation: The result of adding two or more numbers together is a sum.
 
        
                    
             
        
        
        
Answer:
4/8
Step-by-step explanation:
If you simplify it you get 1/2
 
        
             
        
        
        
It's either A or C but correct me if I'm wrong :)
        
             
        
        
        
Let G be some point on the diagonal line away from point E.
Angle DEG represents angle 1. 
We're given that angle DEF is a right angle which means it's 90 degrees. Angle DEG is some angle smaller than 90 degrees. By definition, that must mean angle 1 is acute. Any acute angle is smaller than 90 degrees. There's not much else to say other than this is just a definition problem. 
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Extra side notes:
If angle 1 was a right angle, then that would mean angle GEF would have to be 0 degrees; however the diagram shows this isn't the case. 
If angle 1 was obtuse, then there's no way we'd be able to fit it into angle DEF. In other words, there's no way to have an angle larger than 90 fit in a 90 degree angle.