Cellular respiration is divided into the following four stages: 
1. Glycolysis 
2. Pyruvic acid metabolism 
3. Krebs cycle 
4. Oxidative Phosphorylation 
Identify the option that includes all stages in which carbon dioxide is not produced. 

• A. 1 and 2
• B. 2 and 3
• C. 3 and 4
• D. 1 and 4

Answer: (D)