If a person drops or permits destructive or injurious material on a highway, they must __________ remove the material.

The requirement for a person who drops or allows destructive or injurious material on a highway to remove the material "immediately" underscores the urgency of addressing such situations. This term signifies that there is no time to waste in making the area safe for others, as left unattended, such materials could lead to accidents or injuries.

The use of "immediately" conveys the expectation that the action must be taken without delay, reflecting the priority of public safety in traffic regulations. This sense of immediacy is crucial in traffic management and law enforcement to mitigate hazards that could affect drivers and pedestrians.

In contrast, terms like "promptly," "carefully," or "quickly" may imply some degree of flexibility in timing and urgency, which does not align with the legal expectation of addressing potentially dangerous situations as soon as they arise. Therefore, "immediately" is the most accurate term to encapsulate the necessary response to such incidents.