AP BIOLOGY

Detailed explanation-1: -Therefore the answer is B-anaerobic eukaryotes.

Detailed explanation-2: -The first bacteria to appear on Earth, some 3.8 billion years ago, had no choice but to be anaerobic, because the atmosphere at that time contained no oxygen.

Detailed explanation-3: -Genetic comparisons suggest that the oldest, most primitive bacterial lineages were anaerobic and the ability to survive in the presence of oxygen evolved separately in different lineages.

Detailed explanation-4: -Microbial mats or large biofilms may represent the earliest forms of prokaryotic life on Earth; there is fossil evidence of their presence starting about 3.5 billion years ago.

Detailed explanation-5: -The earliest life forms we know of were microscopic organisms (microbes) that left signals of their presence in rocks about 3.7 billion years old.