A Cell Is Placed into a 1 Millimolar Solution of Substance

Multiple Choice

A cell is placed into a 1 millimolar solution of substance X and over time you witness the concentration of X inside the cell increase to 5 millimolar.The best explanation for this is:

A) X is moving into the cell by simple diffusion
B) X is moving into the cell by diffusion through a protein channel
C) X is moving into the cell by facilitated diffusion
D) X is moving into the cell by primary active transport
E) It is not possible to tell which mechanism is responsible for the transport of X