Identify the missing reagent/condition in the following reaction:
$CH_3CH_2OH \xrightarrow{?} CH_3CH_2-O-CH_2CH_3$

• A
  $Conc. H_2SO_4, 413 \ K$
• B
  $Conc. H_2SO_4, 443 \ K$
• C
  $H_3PO_4, 300 \ K$
• D
  $NaOH, 298 \ K$