Answer:
nuclear fusion
Explanation:
When the density and temperature at the core of the gravitationally collapsing nebula reaches values when nuclear fusion is triggered and sustained, that marks the birth of the star.
 
        
                    
             
        
        
        
Answer:Its B 
Explanation:All vegation decay releases CO2 , Increasing Greenhouse gasses! , Hope that helped :)!
 
        
             
        
        
        
Biologist
study life to the extent to which they can uncover, unearth and investigate unseen,
latent and concealed life forms that are still many in number, these crawling
and under the water creatures. And in experimental sense, many biologists are
guided by the ethics in researching life forms. This is to protect and inhibit
other biologist in killing thousands of these living organisms and prevent them
from becoming extinct. Remember that biologists or any other scientists study
because of knowledge and to contribute to the scientific world of making the
ecosystem including us into a much better and cultured place and not the
opposite. 
Hence, there are non-experimental and experimental approaches which
are all subject to ethics. In exploring life forms, it is quite unlimited but
studying life forms in experimental sense, it is somehow depends on the number
of species that the biologists’ study.