Answer:
Earth rotation...is the reason
 
        
             
        
        
        
 A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms.
 
        
             
        
        
        
Answer:
c.earths moon
Explanation:
earths moon rotates around the earth and causes night to the earth ,as we all know,so c. is the answer.
 
        
                    
             
        
        
        
<span> Biological disadvantages; people will be able to rid themselves of diseases or provide themselves with superior genes. </span>
        
             
        
        
        
Answer:
Parenchyma cells are the abundant cells that make up ground tissues in plants.They are flat at point of contact.they have thin primary cell walls and have large vacuoles for storage of food.In leaves they are called mesophyll and are sites of photosynthesis.In other parts they are sites for respiration and protein synthesis.
Sclerenchyma cells are cells with rigid secondary cell walls.Their cell walls are hardened with lignin which is the main chemical component of wood.Mature sclerenchyma cells cannot elongate and most of them are dead.
Explanation: