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: Physiology
Which of the following is not a monomeric intermediate filament? 
Select and explain. 
A. Vimentin, B. Keratin, C. Desmin, D. Tubulin
D: Tubulin
Answer: D: Tubulin 
Explanation: Ans. D. TubulinThe building block of a microtubule is the tubulin subunit, a heterodimer of a- and b-tubulin.