The answer is a. Nitrogen
        
             
        
        
        
Answer & explanation:
Mountains are large formations of land at high altitudes, where conditions are often difficult. For example, cold weather and food shortages.
In the highest areas of the mountains, animals such as vultures, eagles, hawks and other birds of prey usually prevail.
In addition, it is common for the sides of the mountains to be covered with forests. In these areas it is possible to observe the predominance of animals such as moose, goats, sheep, skunks, llamas and lynx. This group has good climbing skills and manages to stay in the side of the mountains and in some high areas (not as high as the previous group).
Meanwhile, in the lower parts of the mountains, where the forest is denser, it is possible to observe the predominance of snakes, wolves, marmots, foxes, etc.
 
        
             
        
        
        
Answer:
They have  helical thickening of lignin in their walls to prevent collapse
Explanation:
the primary function of Xylem and its conducting vessels tracheids is to provide  support and tranport  water and  minerals  in plants.
 Xylem vessels  have layers of dead materials in the walls called LIGNIN.   Lignin is a polymer; a  very strong, hard materials that stop water passage  through it,because it contains dead cells, 
Therefore  the presence of  deposit of these strong  impermeable, ligified  walls  in its  walls  prevent its collapse during mass flow of water of transpiration pull.
 
        
             
        
        
        
Answer:
The definition of trade off is an exchange where you give up one thing in order to get something else that you also desire. An example of a trade off is when you have to put up with a half hour commute in order to make more money.
Explanation: