to delay or trigger the next phase of cycle
 
        
             
        
        
        
The rods originally contain the fuel for nuclear reactions, which mean they are highly radioactive. The radiation they emit is very dangerous and harmful to all types of life; therefore, they must be handled with care and disposed of properly to minimize damage because of them.
        
                    
             
        
        
        
Answer:
irreversible chemical change
Explanation:
A chemical change always results in a new substance and as it is not possible to reverse it, it is an irreversible chemical change.
I hope you understood :)
 
        
             
        
        
        
Answer:
The correct answer will be option-A 
Explanation:
The ecological population is the group of the organism belonging to the same species which live or is found in the particular area and can interbreed.
Since in the given question, the redwood trees live in the same geographical area (forest) which can interbreed shows the population. The other examples represent the community which consists of more than one species.  
Thus, option-A is the correct answer.