The answer to this question would be: excess fluoride intake
The toothpaste has a high amount of fluoride and will increase the blood fluor level. Excess fluoride intake in children can cause fluorosis which was the brown staining of teeth because fluor is deposited in the growing teeth. Fluorosis can happen in children with <8-year ages.
        
             
        
        
        
Abiotic factor means no living so your answer is water :)
        
             
        
        
        
Answer:
Explanation:
The major reason is due to the different and diverse possible arrangements of chromosomes into gametes.
 
        
             
        
        
        
A method or procedure consisting of testing experimenting, and measuring trying to prove a hypothesis.