Question

which of the following structures is shaped like a hollow cylinder made out of tubulin proteins?
microtubules
intermediate filaments
microfilaments
flagella

Explanation:

Microtubules are hollow cylinders made of tubulin proteins. Intermediate filaments and microfilaments have different structures. Flagella contain microtubules but are not just simple hollow - cylinder structures of tubulin.

Answer:

Microtubules