Correct chronological order of the steps occurring during gene therapy are
$I$. Lymphocytes are obtained from the patients
$II$. Lymphocytes are transferred to the culture dishes
$III$. Lymphocytes are transfected with the normal $ADA$ genes
$IV$. The transfected cells are returned to the patients
The chronological order should be

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