In this whole little thing you got going its a
        
             
        
        
        
Answer:
D. to increase their surface area
Explanation:
The usefulness of microvilli to cells that have them is TO INCREASE THEIR SURFACE AREA.
 
        
             
        
        
        
Answer:
B. Living things 
Explanation:
cells are the basic unit of life and function
 
        
             
        
        
        
 Answer: Silicon is classified as a metalloid.
Metalloids are those elements which have properties of metals as well as non-metals. This means that they are intermediate of metals and non-metals. They are also called as semimetals.
Silicon is the typical example of a metalloid. The physical property that it is lustrous is similar to metals, whereas it is easily cracked, therefore, it is brittle like non-metals.
Thus, it is classified as a metalloid.