Hello to answer your question.
A is correct
 But more likely forest fires would be the culprit because the trees produce O2
 so when the are burnt, it would be like everybody o this earth breathed out at   once causing CO2 to be released in to the atmostphere in a big burst
         Signed by, Virtuoso Sargedog
        
             
        
        
        
A blue shift is any decrease in wavelength, with a corresponding increase in frequency, of an electromagnetic wave; the opposite effect is referred to as red shift. In visible light, this shifts the color from the red end of the spectrum to the blue end.
 
        
             
        
        
        
Answer:
the process by which heat or electricity is directly transmitted through a substance when there is a difference of temperature or of electrical potential between adjoining regions, without movement of the material.