What is it i hope i can helps you:(
 
        
             
        
        
        
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 minimum difference is already the value of 1
Explanation:
When the pH is not balanced between the extracellular and intracellular environment, the cell could go into shock, that is why in the face of the minimal differences in pH between the internal or external environment, the proton pump is activated, this is how the hydrogen ion or positively charged protons cross the membrane and indirectly generate ATP molecules.
 
        
             
        
        
        
Answer:
High Temperature, X-rays, Radiation, Some Chemicals
Explanation:
In general, mutations happen due to some error in the DNA duplication process, however, there are certain factors in the environment that can increase the incidence rate of these genetic errors. Excessive exposure to x-rays, substances present in smoke, ultraviolet light, excessive temperature, nitrous acid and some dyes present in food, for example, can favor the appearance of mutations. In general, we can say that mutations can be caused by high temperature, X-rays, radiation, some chemicals.
 
        
             
        
        
        
NAD is the electron carrier which is used in redox reactions in cellular respiration