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
Biotin is required for the activity of 
Select and explain. 
A. Pyruvate carboxylase, B. Lactate dehydrogenase, C. Succinate thiokinase, D. Phosphohexose isomerase
A: Pyruvate carboxylase
Answer: A: Pyruvate carboxylase 
Explanation: Mitochondrial pyruvate carboxylase catalyzes the carboxylation of pyruvate to oxaloacetate, an ATP-  requiring reaction in which the vitamin biotin is the coenzyme.
Biotin binds CO2 from bicarbonate as carboxybiotin prior to the addition of the CO2 to pyruvate.
The resultant oxaloacetate is reduced to malate, exported from the mitochondrion into the cytosol  and there oxidized back to oxaloacetate.

Key Concept:
Biotin is the co-enzyme for pyruvate carboxylase which carboxylates pyruvate into oxaloacetate
Ref : Harper’s illustrated biochemistry, 31st edition.