What should a firefighter do before stepping off a ladder, parapet wall, or other place of safety onto the roof of a burning building, especially if the roof surface is obscured by smoke or darkness?

A. Ensure the safety of all personnel who are assisting.
B. Direct a fire stream into an existing vertical exhaust opening.
C. Sound the roof for structural integrity by striking with an axe.
D. Direct a fire steam into an existing horizontal exhaust opening.

C