Recombination refers to the process by which the fragments of the DNA molecules (either from one or two species) are isolated, cut and inserted into the host strand. The inserted DNA fragment may be directly replicated on its own or through the integration with the host chromosomes.The resulting strand will difer from the old strand.  
        
                    
             
        
        
        
Concerning the balance of pollutants in the biosphere, Scientists have proved that the natural system of the earth is overwhelmed by pollution.
 
        
             
        
        
        
Every soil<span> originally formed from parent material: a deposit at the Earth's surface. The material could </span>have<span> been bedrock that weathered in place or smaller materials carried by flooding rivers, moving glaciers, or blowing winds.</span>
        
                    
             
        
        
        
Answer: C) a factor that may affect an experiment or investigation
Explanation:
This is the best answer. A and B can be eliminated. D describes a controlled variable which is more specific than a scientific variable, thus C is the best answer. It is the best description of  just a scientific variable.
 
        
                    
             
        
        
        
Answer:
The pitch is the independent variable.
The dogs are the dependent variable.
Explanation:
An independent variable is something that you can control such as how high or low the pitch is. The dependent variable is the variable that is dependent on the independent variable. The dependent variable is the one that shows the results.