Answer:
CO2 is a compound, it has 2 atoms of oxygen, and is made up of oxygen and carbon
Explanation:
 
        
             
        
        
        
Natural disasters weaken a community's social infrastructure because
D. Natural disasters can cause billions of dollars in property damage<span>.
The social infrastructure of a community includes social assets such as schools, hospitals, prisons and community housing. Such places are damaged in natural disaster, adversely affecting the community.</span>
        
                    
             
        
        
        
They could improve the experiment that they made by adding another variable such as: watering the plants with fresh water. This way they could have a better comparison how plants grow based on the type of water they are exposed with.  
        
             
        
        
        
Answer:
There are many green house gases and carbondioxide is one of them. Green house gas has the ability to stop the heat from going to the atmosphere. This heat energy reduces the atmospheric carbondioxide to dissolve in the ocean water so more concentration of carbondioxide is present in the atmosphere which stop the reflected sunlight rays into the space and thus increase the temperature of the earth surface. This increase in temperature called global warming. 
 
        
             
        
        
        
Answer:
The correct answer is - Fossil fuels are cheaper than alternative forms of energy.
Explanation:
Fossil fuels are made by the natural process in a longer time period such as anaerobic decomposition of the dead organism like plants, and animals. These plants and animal's decomposed organic matter pilled up to form coal, or natural gases or crude oil.
By the use of such fuels the reserves are continuously depleting and will be no longer available in the future if not managed properly as it can not be renewed. Fossil fuels increases the green house gases in environment and affect it by incresing carbon in atmosphere. However, these fuels are cheaper in comparision of other fuels.
Thus, the correct answer is - Fossil fuels are cheaper than alternative forms of energy.