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
Which one of the following enzymes provides a link between glycolysis and the citric acid cycle? 
Select and explain. 
A. Lactate dehydrogenase, B. Pyruvate Kinase, C. Citrate synthase, D. Pyruvate dehydrogenase
D: Pyruvate dehydrogenase
Answer: D: Pyruvate dehydrogenase 
Explanation: PDH complex consist of 3 Enzymes and 5 Coenzymes
Three enzymes are:

Pyruvate Dehydrogenase bound to Thiamin Diphosphate
Dihydrolipoyl Transacetylase, the prosthetic group is oxidised Lipomide
Dihydrolipoyl  Dehydrogenase, contains FAD.

Coenzymes (very important)

Thiamine Diphosphate (TDP)
Lipomide
Coenzyme A
FAD
NAD

Key Concept:
 Pyruvate Dehydrogenase  which converts pyruvate to acetyl CoA provides a connecting link between glycolysis and citric acid cycle.