[QA] The fire must have been started on purpose; otherwise, it couldn’t have caused so much damage.

Question:

The fire must have been started on purpose; otherwise, it couldn’t have caused so much damage.

• A.
  The fire might have been very serious if nobody had tried to prevent it.
• B.
  Seeing that it destroyed so many things, the fire can’t have been accidental
• C.
  If someone were to start a fire there, it could prove highly damaging
• D.
  No one can say for sure how the fire broke out, but the harm it did is obvious.