Answer:
Letter B.
Step-by-step explanation:
Aquaporins, also known as "water channels," are the main transport of water through the membranes of plant, animal, and bacterial cells. These channels allow the water to travel into and within cells and, at the same time, exclude the passage of ions and solutes.
What makes letter B the correct answer, is the form of transport and shape of the channel that allow water according to the osmotic gradient. In this model, letter A shows simple diffusion, while C and D seem to illustrate gated channels.