Approximately 99% of the Microbes in the Intestines Are Obligate

Approximately 99% of the microbes in the intestines are obligate anaerobes. We have plenty of blood vessels that can bring oxygen to the tissues of the intestines. Why would there be obligate anaerobes within these areas?

A) The bacteria in the intestines are protected from exposure to the oxygen in the tissues by the lining of the intestines.
B) The bacteria consume all the oxygen in the tissue areas brought by the blood vessels, creating an anaerobic environment.
C) While the blood vessels supply oxygen to the tissues of the intestines, the inner area where the bacteria reside is NOT supplied with blood/oxygen. Since it's deep within our bodies, there's no chance for oxygen to get into these inner areas of the intestinal tube, creating a highly anaerobic environment.
D) The aerobic microbes are outcompeted for nutrients in these areas by the anaerobic microbes.