The lateral movement of transmembrane proteins can be restricted by several different mechanisms. which mechanism best describes the process by which focal adhesions are formed to promote cell motility?
(a) proteins are tethered to the cell cortex
(b) proteins are tethered to the extracellular matrix
(c) proteins are tethered to the proteins on the surface of another cell
(d) protein movement is limited by the presence of a diffusion barrier

B. Proteins are tethered to the extracellular matrix

Explanation:

The assembly of nascent focal adhesions is strongly dependent on the process of actin flow, happening in migrating cells when the actin filament polymerize at the edge and flow back towards the same cell's body.

That is what causes the traction needed for migration, when the focal adhesion works a support when it tethers to the extracellular matrix and impedes the backward move of actin, generating the traction force needed at the point of contact to move the cell forward.

what's the question?

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).