I’m pretty sure the C molecules are carbon dioxide? And the O molecules are Oxygen? yeah.. I’m pretty sure
        
             
        
        
        
All plants have a cell wall, all mammals have a cell membrane. a cell membrane is semi-permeable it allows mammal cells to absorb needed nutrients, oxygen and deposit waste into the blood stream where it is excreted through urine and feces. a plant cells nutrients are absorbed through the root system and leaves, waste is excreted in the form of oxygen through the plant itself.
        
             
        
        
        
Answer:
the first wave of extinction may be related to rapid cooling at the end of the Ordovician Period, and the second phase is widely regarded as having been caused by the sea-level fall associated with the glaciation.
 
        
             
        
        
        
The carbon footprint can be decreased by a great amount if the incandescent bulbs are replaced with the compact fluorescent bulbs. The compact fluorescent bulbs uses approximately seventy five percent less energy than the incandescent bulbs as they do not use heating mechanism to light. This leads  to less emission of the green house gases and thereby reducing the carbon footprint. 
Hence, the correct answer is 'option a - replacing incandescent bulbs with compact fluorescent bulbs'.