Read the following statements carefully and select the correct option.
$I.$ The medulla is connected to the spinal cord.
$II.$ Medulla contains controlling centers for respiration,cardiovascular reflexes and gastric secretion.
$III.$ Cerebellum has very convoluted surface in order to provide the additional space for more neurons.

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