What is a backdraft? (Multiple Choice)

What is a backdraft?
 
  A) A rapidly occurring transitional event in the development of a compartment fire
  B) The condition whereby unburned fuel (pyrolyzate) from the originating fire has accumulated in the ceiling layer to a sufficient concentration that it ignites and burns
  C) The ignition of unburned pyrolyzates due to sudden influx of air which ignites and results in an extremely rapid burning of gases/pyrolysis products being forced out through an opening
  D) The sudden ignition of a diffused fuel suspended in the atmosphere