Refer to the following statements for agarose-gel electrophoresis :
$(a)$ Agarose is a natural polymer obtained from sea-weed.
$(b)$ The separation of $DNA$ molecules in agarose-gel electrophoresis depends on the size of $DNA$.
$(c)$ The $DNA$ migrates from negatively-charged electrode to the positively-charged electrode.
$(d)$ The $DNA$ migrates from positively-charged electrode to the negatively-charged electrode.
Choose the most appropriate answer from the options given below :

• A
  $(a)$ and $(b)$ only
• B
  $(a), (b)$ and $(c)$ only
• C
  $(a), (b)$ and $(d)$ only
• D
  $(b), (c)$ and $(d)$ only