Answer: I think is B or A
Step-by-step explanation:
 
        
             
        
        
        
Using the Pythagorean theorem:
a^2 + b^2 = c^2 
A and B are the sides and c is the hypotenuse.
4^2 + 5^2 = c^2
Simplify:
16+25 = c^2
41 = c^2
Take the square root of both sides:
c=√41
 
        
                    
             
        
        
        
Complementary angles add up to 90°
∠BDC + ∠CDA = 90°
Answer: ∠BDC
        
             
        
        
        
I believe it's the first option. Hope this helps.