The solid liner cytoskeleton elements having a diameter of 6 nm and made up of a single type of monomer are known as
A. Microtubules
B. Microfilaments
C. Intermediate filaments
D. Lamins

Hint: In the eukaryotic cells the cytoskeleton is a unique part present in the 3 dimensional form and filled with the cytoplasm. And muscles or skeleton help to move and stabilize the body. Cytoskeleton are the polymer subunits that are present in the long fibers of the cytoskeleton. Microfilaments, microtubules, and intermediate filaments are the primary types of fibers that comprise the cytoskeleton.

Complete answer:
Cells are remarkably motile and in vertebrate embryo neural cells are present that leave the development of the nervous system but migration of the width of the embryo. An actin monomer binds a molecule of ATP before incorporated into the filaments. The role of actin assembly similar to the GTP in the microtubules and tubulin act as a GTPase and actin act as an ATPase.
With the \[{S_1}\] myosin the electron micrographs of short actin filaments used to nucleate actin polymerization. Most of the skeleton muscles are anchored to bones derived from their name from the fact that bones move. Highly unorthodox structure present in the muscles skeleton. It is also called a muscle fiber because of cylindrically shaped, typically thick and hundreds of nuclei.

Therefore the correct option is (B).

Note: The thread like protein structure 3-6 nm in diameter and composed of contractile protein known as the actin. And microtubules composed of protein subunits of the protein tubulin 20-25 nm in diameter and termed as alpha beta subunits. Intermediate filaments provide the tensile strength to the cells and have 10 nm diameter and lamin protein present inside it.