Answer:
Aluminum
Explanation:
The density of Aluminum is 2.7 g/cm3 
We know the volume and mass of the unknown metal, as density is mass/volume:  81g/30cm3 = 2.7 g/cm3 which is the density of Aluminum :)
 
        
                    
             
        
        
        
I believe it is a combination of polygenic inheritance and environmental factors. Several genes control the height in humans, giving an overall normal distribution. Environmental factors on the other hand such as nutrition smooth out the curve. It is therefore important to note that Human height is a quantitative, or metric trait, that is, a characteristic that is measured in quantity, and is controlled by multiple genes and environmental factors. 
        
             
        
        
        
They should be carbohydrates, fats (lipids) and protein. they are labelled as primary food substances and they're essential to life. they can provide energy and raw material for life processing. although mineral ions and vitamin are important too, but they only need a small amount.
        
             
        
        
        
Polarity- Epithelium is arranged so there is one free surface (apical surface) and one attached surface (basal surface)
Cellular nature– Cells in epithelium fit closely together side by side and sometimes atop each other to form sheets of cells.