When a Cell Is in Equilibrium with Its Environment,which of the Following

When a cell is in equilibrium with its environment,which of the following occurs for substances that can diffuse through the cell?

A) There is random movement of substances into and out of the cell.
B) There is directed movement of substances into and out of the cell.
C) There is no movement of substances into and out of the cell.
D) All movement of molecules is directed by active transport.
E) Molecules move up their concentration gradient.