Which of the following statements is correct about passive diffusion?

A)It requires an expenditure of energy by the cell.
B)It is a process in which molecules move from a region of higher concentration to a region of lower concentration (or down a concentration gradient).
C)It is a process in which molecules move from a region of lower concentration to one of higher concentration (or up a concentration gradient).
D)It may require a transport protein.
E)It involves movement of molecules down a concentration gradient and may require a transport protein.