Cell membrane is selectively permeable because

• A

  it is made up of selected organic molecules
• B

  it does not allow transport of some substances from region of higher concentration to the region of lower concentration
• C

  the movement of organic molecules occurs only at specific concentration
• Correct answer
  D

  it allows the movement of certain molecules in and out of the cell while the movement of other molecules is prevented

Hence, the correct answer is option: 'D'.