Refer to the Numbered Steps in the Figure When Answering

Multiple Choice

Refer to the numbered steps in the figure when answering the question. Two carbons in the form of acetyl- CoA enter the Krebs cycle by joining with oxaloacetic acid, a 4- carbon molecule. During which step does carbon leave the Krebs cycle in the form of CO₂?

A) step 1
B) step 3
C) step 4
D) step 1 and step 3 and step 4
E) step 3 and step 4