Consider the following statements regarding gymnosperms and choose the correct option.
$I.$ In gymnosperms,the male and female gametophytes have an independent existence.
$II.$ The multicellular female gametophyte is retained within the megasporangium.
$III.$ The gymnosperms are heterosporous.
Of these statements:

• A
  $I$ and $II$ are true but $III$ is false
• B
  $I$ and $III$ are true but $II$ is false
• C
  $II$ and $III$ are false but $I$ is true
• D
  $II$ and $III$ are true but $I$ is false