The correct answer is by facilitated diffusion.
The procedure of continuous passive transport of ions or molecules through a semi-permeable membrane with the help of particular transmembrane integral proteins is known as facilitated or passive-mediated transport or facilitated diffusion.
It is a modification of osmosis incorporating a proteinaceous channel via which an extracellular solute can enter a cell in the absence of energy.
Mass transit can help reduce air pollution in urban cities because there are fewer cars on the roads, creating less pollution.