A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms, when they share electrons, is known as covalent bonding.
        
                    
             
        
        
        
Answer:
Granites and rhyolites consist predominantly of quartz and potash feldspar; gabbros and basalts, predominantly of pyroxene and plagioclase feldspar. Other rock types have intermediate mineral compositions.
Explanation:
 
        
             
        
        
        
Here are a few general differences between the planets Venus and Mars :
<span>Venus is hotter than Earth and is the hottest planet in the solar system (hotter than Mercury), Mars is colder than Earth.Venus is the second planet from the Sun , Mars is the fourth planet from the Sun. Venus is an inferior planet from Earth, Mars is a superior planet .<span>The astronomical (and astrological) symbol of Mars is the following one (Free image from Wikipedia):</span></span>
 
        
                    
             
        
        
        
The replacement rate is the level at which a population remains stable.   
<span>Replacement rate (level) is the fertility rate and represents the average number of children born per woman at which a population<span> exactly replaces itself from one generation to the next (without migration). More precisely, </span>it is the amount of fertility needed to keep the population the same, from generation to generation. As a result of the total <span>fertility rate,</span><span> there will be no increasing or decreasing of the population, it will be stable. </span></span>
        
             
        
        
        
Answer: D: They are closed at one end
Explanation:
"Lymphatic Capillaries" are tiny, thin walled microvessels located in spaces between cells and their main function is to drain and process extracellular fluid. 
They are larger than blood capillaries and have "closed ends". Their unique structure permits interstitial fluid to flow into them but not out. Thus their ends are closed unlike the loop structure of blood capillaries.