To answer this question we need to analyze each available option:
a) Phospholipids are molecules that conform the plasmatic membrane and act as barrier therefore this is incorrect.
b) Gated proteins, these proteins allow pass ions and a very specific so even when this could be an option is not entirely correct.
c) Carrier proteins, these proteins are involved in facilitated diffusion and active transport processes, therefore this is incorrect.
d) Channel proteins, these proteins due to their specific structure are embedded in the cell membrane and provide a passage for hydrophilic compounds, therefore this is the correct answer