Point source means: the pollution that comes from a single point (examples)
Sewage pipes releasing sewage into a ditch
Smokestack style factory chimneys 
Oil pipes
Pollution which is caused by rain fall or snow melting into the ground. As the runoff moves, it picks up and carries away natural and human made pollutants, Finally reaching a lake, river, ocean, groundwater. 
        
             
        
        
        
<span>D a rigid cell wall which provides structure and support
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The answer is a. the abiotic components of an ecosystem
        
                    
             
        
        
        
Can you provide more specific details? I’m not even sure what this question is about.
 
        
             
        
        
        
Answer: 500 velocity 
Explanation: Wave velocity (m/s) =Wavelength (m) * Frequency (Hz) Example calculation. I found this by using calculation of wavelength times frequency and the answer will be your velocity.