What is the process by which substances move across the membrane through channels without using energy

Because facilitated diffusion is a passive process, it does not require energy expenditure by the cell. Water also can move freely across the cell membrane of all cells, either through protein channels or by slipping between the lipid tails of the membrane itself.

hope this is the right answer

correct answer is option a.

tropopause, stratopause and mesopause have all in common aspect that is point of maximum temperature in its layer of the atmosphere. all layers of atmosphere observe abrupt change in temperature. tropopause is the boundary between troposphere and stratosphere. stratopause is the boundary between stratosphere and mesosphere. mesopause is the boundary between mesosphere and thermosphere. these all boundaries are ranges between altitude of 0 to 80 km.

i think that d. wind is the answer.   i missed the question when i answered a. currents.