Consider the following statements:
$I$. They reproduce asexually by non-motile spores and sexually by non-motile gametes.
$II$. In this class,sexual reproduction is oogamous and accompanied by complex post-fertilisation developments.
$III$. The common members are $Polysiphonia$,$Porphyra$,$Gracilaria$ and $Gelidium$.
The above characteristics belong to which class of algae?

• A
  Chlorophyceae
• B
  Phaeophyceae
• C
  Both $(a)$ and $(b)$
• D
  Rhodophyceae