The aerated upper layer of soil is likely to have ________ concentrations of H₂ for aerobic H₂-oxidizing Bacteria, so these bacteria likely ________.
A) high / thrive in such conditions by not competing with chemoorganotrophs B) high / generate important reducing equivalents as byproducts for other microorganisms in the soil C) low / do not occur in such habitats D) low / will need a chemoorganotrophic way to grow as well