Ascariasis is caused by an endoparasite of human $...A...$ commonly called $...B...$ Here $A$ and $B$ refer to:

• A
  $A$ - Ascaris suum; $B$ - tapeworm
• B
  $A$ - Ascaris; $B$ - roundworm
• C
  $A$ - Ascaris worm; $B$ - flatworm
• D
  $A$ - Ascaris; $B$ - liver worm