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. What is the best explanation for this observation?

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) Water is leaving the cell by osmosis.