In the structure of diborane :
 

• A

  all hydrogen atoms lie in one plane and boron atoms lie in a plane perpendicular to this plane.

• B

  2 boron atoms and 4 terminal hydrogen atoms lie in the same plane and 2 bridging hydrogen atoms lie in the perpendicular plane.
   

• C

  4 bridging hydrogen atoms and boron atoms lie in one plane and two terminal hydrogen atoms lie in a plane perpendicular to this plane.
   

• D

  all the atoms are in the same plane.