Bioinformatics Has Identified Some Enzymes Used in the Citric Acid

Multiple Choice

Bioinformatics has identified some enzymes used in the citric acid cycle in primitive bacteria.Once such a cycle utilized many of the citric acid cycle intermediates but occurred in the reverse direction.Researchers suspect which of the following based on this information?

A) Researchers suspect that the "original" citric acid cycle was used by all species.
B) Researchers suspect that portions of the reverse cycle may have been responsible for fixing CO₂
C) Researchers suspect that early methods for converting pyruvate to acetyl CoA did not exist.
D) Researchers suspect that the current "clockwise" version of the citric acid cycle could be used to help humans feed off CO₂.
E) Researchers suspect that primitive prokaryotic use of the citric acid enzymes were focused on the production of CO₂ rather than the use of CO₂.