Since the reaction gives off heat energy it is considered to be an exothermic reaction
        
             
        
        
        
Answer: 
The answer is 
D. Main sequence
Explanation:
Main sequence stars can be between one thousand times dimmer and one million times brighter than the Sun. 
What is main sequence stars? 
A main sequence star is any star that is fusing hydrogen in its core and has a stable balance of outward pressure from core nuclear fusion and gravitational forces pushing inward.
 
        
             
        
        
        
Answer: Scientists use the term bioenergetics to describe the concept of energy flow (Figure 4.2) through living systems, such as cells. Cellular processes such as the building and breaking down of complex molecules occur through stepwise chemical reactions. Some of these chemical reactions are spontaneous and release energy, whereas others require energy to proceed. Just as living things must continually consume food to replenish their energy supplies, cells must continually produce more energy to replenish that used by the many energy-requiring chemical reactions that constantly take place. Together, all of the chemical reactions that take place inside cells, including those that consume or generate energy, are referred to as the cell’s metabolism.
 
        
             
        
        
        
Answer: An atom can join with other kinds of atoms.
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