Answer: The answer is D: 300,000km/s
Explanation:
 
        
             
        
        
        
I would say Option B) because Option C) is wrong since matter cannot be created. A closed system does not exchange matter so it's not Option D). Since an island is an isolated area, Option A) is wrong.
        
                    
             
        
        
        
X - rays are highly penetrating electromagnetic radiations that are formed when the cathode rays strikes a dense metal. 
It has many characteristics such as :
- travels with the speed of light.
 
        
             
        
        
        
Answer:
a luminous ball of plasma