Microfilament assembly and disassembly are dependent upon the concentration of

ATP-actin monomers.

Explanation:

Actin Microfilaments are mainly located in the cell periphery, below the membrane and are formed by strands of the actin protein, braided in a helix of about 50 Å in diameter and variable length, whose stability is due to the presence of ATP and ions of calcium Associated with myosin filaments, they are responsible for muscle contraction. Other functions for example, give flexibility to red blood cells, help cytokinesis in cell division, participate in ameboidal movements (pseudopods) of some unicellular organisms.

Actin, in itself, is a dynamic structure that polymerizes and depolymerizes according to the conditions of the medium.

It has also been found that the polymerization is reversible, and that it depends on the amount of free monomers. The regulation of the assembly and disassembly of the monomers occurs as follows: it reaches a certain concentration of free ATP-actin monomers, the actin begins to polymerize. As the monomers are assembled, their concentration in the cytoplasm decreases. When the concentration of monomers is low, up to a certain value, depolymerization begins.

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.