This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Building block for fatty acid biosynthesis is: 
Select and explain. 
A. NADH, B. Acetyl-CoA, C. Acyl-CoA, D. Acetate
B: Acetyl-CoA
Answer: B: Acetyl-CoA 
Explanation: Fatty acid biosynthesis in the cytosol requires a sufficient concentration of NADPH and acetyl CoA.NADPH is generated in the cytosol by the pentose phosphate pathway, and by the malic enzyme which oxidizes malate into pyruvate and CO2, generating NADPH.