It is b. the PH level decreases causing the solution to become more acidic. 
        
                    
             
        
        
        
Astronomers use the Doppler effect<span> to measure the frequency of light waves as an object is moving with respect to the observer</span>
        
             
        
        
        
Observation, hypothesis, experiment is the correct answer
        
                    
             
        
        
        
Answer
 Used up faster than they are able to be replaced
Explanation:
The word renewable itself mean non-depletable or naturally replenish able. They cause little to no  environmental impact that it can be used for long term. They are available in plenty and cannot be used up in quick time. Hence option a is correct. Rest all are correct about  characteristic of a renewable resource
 
        
             
        
        
        
The nucleus is the center of the atom where the protons and neutrons can be found.