Which of the following statements are correct?
$I$. Binding of inhibitor at allosteric site changes the shape of the active site.
$II$. Shape of the receptor does not change after attachment of chemical messenger to it.
$III$. $A$ chemical messenger gives message to the cell by entering it.
$IV$. Erythromycin is an example of bacteriostatic antibiotic.

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