$I.$ In $C_{3}$-plants,the Calvin pathway takes place in mesophyll cells.
$II.$ In $C_{4}$-plants,the Calvin pathway takes place in the mesophyll cells.
Which of the following statements is true?

• A
  Statement $I$ is incorrect,$II$ is correct.
• B
  Statement $II$ is incorrect,$I$ is correct.
• C
  Both are incorrect.
• D
  Both are correct.