Which of the Following Descriptions of Movement of Molecules Across

Which of the following descriptions of movement of molecules across the plasma membrane is correct?

A) if two similar molecules can both combine with the same carrier, the presence of one of these molecules decreases the rate of entry of the other.
B) in simple diffusion, the rate of transport of a molecule is directly proportional to the molecule's extracellular concentration.
C) when a carrier becomes saturated, the maximum rate of transport is reached.
D) two of these answers.
E) all of these answers.