I would say the answer is A.
Carbon fixation<span> refers to the conversion process of inorganic </span>carbon<span> (</span>carbon <span>dioxide) to organic compounds by living organisms. The most prominent example is photosynthesis, although chemo synthesis is another form of </span>carbon fixation<span> that can take place in the absence of sunlight.</span><span />
B) the bacteria that live in the intestine of a rabbit
A- Drilling through the Earth to reach areas is useful but expensive