Genes are responsible for every cellular differences in a way that it is active on the same type of cell and inactive in another type of cell. The reason for genes to be active in a specific cell is because of enzymes or protein that turn it on.
        
             
        
        
        
Exposure to infrared light can heat the lens of the eye and produce cataracts over the long term. 
 
        
                    
             
        
        
        
Answer: a.
Explanation:
The proficiency to be more professional and confident using one hand instead of the other for activities such as writing and throwing a pitch is called handedness.
Handedness begins to develop before birth. Handedness is inheritable and  evident from early childhood. handedness is related to variations between the brain's right and left halves (hemispheres). The<em> the left hemisphere regulates the action of right side of the body while right hemisphere controls movement on the left side of the body</em>. 
So in handedness, one half of the brain regulates more skilled motor action.
Hence, teh correct option is a.
 
        
             
        
        
        
4 chambers in the heart and mammals and birds have the same number of chambers