The Two Moles of CO₂ Produced in the First Turn

The two moles of CO₂ produced in the first turn of the citric acid cycle have their origin in the:

A) carboxyl and methylene carbons of oxaloacetate
B) carboxyl group of acetate and a carboxyl group of oxaloacetate.
C) carboxyl group of acetate and the keto group of oxaloacetate.
D) two carbon atoms of acetate.
E) two carboxyl groups derived from oxaloacetate.