What roles do membrane proteins play in transport, signaling and structural support?

Membrane proteins are usually embedded in the bi layer structure of the cell membrane. The principal function of membrane protein is that of carrier. They facilitate the entrance of  molecules which can not enter the cell on their own, thus they transport the necessary materials into the cell.
The membrane receptor proteins relay signals between the cell's internal and external environment. In term of support, protein filaments gives structural support to the cell.

We are not able to see the stars. light prevents our seeing the stars. i hope it kinda : )

The answer would be d. pili