In order for a compartment to completely fill up due to flooding, what condition must exist?

Correct Answer: Option B — The compartment must have an opening at the overhead allowing air to escape in addition to having a source of flooding.

For a compartment to fill completely, air must be displaced as water enters. If the overhead remains sealed, trapped air creates a pocket that prevents further flooding. An opening at the overhead is essential to allow air to escape, enabling the water level to rise until the compartment is fully flooded.