Carbon dioxide is part of capturing energy, but it is not the direct source. The direct source in photosynthetic systems, for example, is sunlight. Therefore, a) is UNLIKELY.
Gene flow only occurs between individuals from the same species, because it involves the transfer of alleles and individuals from different species wouldn't be able to do so. Therefore, b) is LIKELY.
Gene flow can act agains local adaptation because it brings new factors, which will again transform the circumstances in which the organismsm are trying to adapt. Therefore, c) is LIKELY.
Chemoautotrophic organisms acquire energy and this energy is accessible to other organisms by consuming the chemoautotrophic ones. So, if they weren't there, there would be no way for ther other organisms to access the energy. Therefore, d) is UNLIKELY