In a $DNA$ molecule,the antiparallel strands mean that:

• A
  The two strands of $DNA$ have phosphate groups at their ends in the same position.
• B
  The two strands of $DNA$ run in opposite directions,with phosphate groups at opposite ends.
• C
  One strand rotates in a clockwise direction.
• D
  One strand rotates in an anti-clockwise direction.