Which of the following statements is/are true?
$I.$ Urine is hypertonic while entering distal convoluted tubule.
$II.$ When the urine moves in the collecting tubule,it becomes hypertonic.
$III.$ Urine is isotonic in proximal convoluted tubule.
$IV.$ Urine becomes more and more hypotonic as it passes through the descending Henle's loop.

• A
  $I$ and $IV$
• B
  $I, II$ and $III$
• C
  $II$ and $III$
• D
  $I$ only