Why are some obligate anaerobes able to grow in tissues (e.g., gum pockets) that are not completely free of oxygen?

A) They have the ability to utilize oxygen intermittently during their growth cycle.
B) These organisms possess enzymes that neutralize oxygen radicals.
C) They form spores that protect them from oxygen damage.
D) These organisms have evolved mechanisms to survive in low-oxygen environments by utilizing anaerobic respiration pathways.