Arrange the following in order of increasing reactivity (least $\to$ most) towards nucleophilic acyl substitution:
$1. CH_3COCH_2CH_3$,$2. CH_3COCl$,$3. CH_3CONHCH_3$

• A
  $1 < 2 < 3$
• B
  $3 < 1 < 2$
• C
  $1 < 3 < 2$
• D
  $2 < 1 < 3$