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 among the following controls is an allosteric inhibitor of TCA cyclea) Pyruvate dehydrogenaseb) Ketoglutarate dehydrogenasec) Isocitrate dehydrogenased) Malate dehydrogenase 
Select and explain. 
A. a, B. b, C. bcd, D. abc
D: abc
Answer: D: abc 
Explanation: Pyruvate dehydrogenase; 'h' i.e., Ketoglutarate dehydrogenase & 'c' i.e., Isocitrate dehydrogenase 

Allosteric modulation in TCA cycle :- Citrate synthase, a-ketoglutarate dehydrogenase, Isocitrate dehydrogenase.
Both allosteric and covalent modulation:- PDH complex.
"Citrate synthase, isocitrate dehydrogenase and a-ketoglutarate dehydrogenase are allosteric enzymes which regulate TCA cycle".