Answer:
The correct option is <em>3. they break down rock into soil in which plants can grow</em>
Explanation:
When a disaster is such huge that even the soil and organic matter get removed from the place, then the succession that will occur in such kind of place will be termed as primary succession. For example, a volcanic eruption or an earthquake.
On the other hand, if after a disaster some of the organic matter remains on the land, then the succession that will occur will be termed as secondary succession. E.g a succession after fire
In primary succession, the pioneer species will be plants that require less soil such as the lichens. The lichens will break down the rocks into the soil and eventually new species of plants will start to grow on the land.
 
        
             
        
        
        
As stated above, breathing is the biological process of inhaling and exhaling of the gases between the cells and the environment. The mechanism of breathing involves various respiratory structures such as the windpipe, lungs and nose. Respiration, on the other hand, is a chemical process that takes place in the cell.
 
        
                    
             
        
        
        
Answer:
convection within the atmosphere
 
        
                    
             
        
        
        
Answer:

Explanation:
An element only has <u>one</u> type of atom and cannot be broken down by chemical means. 
Let's analyze the answer choices. 
1. This has two types of atoms, so it cannot be an element. It has more than one type of atom. 
2. This has two types of atoms that are bonded together. It cannot be an element because there is more than one type of atom and the bonds can be broken. 
3. This has one type of atoms, so it is an element.  
Therefore the best answer choice is 3.