The movement of molecules through a plasma membrane channel protein is always see section 6.

The answer is down the molecule's concentration gradient. To simplify, the movement of molecules through a plasma membrane channel protein is always down the molecule's concentration gradient. In addition, carrier proteins and channel proteins are the two main classes of membrane transport proteins. The carrier proteins bind the specific solute to be transported and undergo a series of conformational changes to transfer the bound solute across the membrane. 

The answer is c : ) hope this answered your question!

Cbecause it is the only one describing a habitat