When a person drops or permits to be dropped injurious material on a highway, they shall ________ remove the material?

The requirement for a person who drops or permits injurious material on a highway to remove it "immediately" emphasizes the urgency of addressing hazards that can pose danger to the public. An immediate response helps to prevent accidents and injuries that could arise from others encountering the hazardous material. This reflects a commitment to public safety and responsibility, highlighting that individuals must take swift action to mitigate risks associated with such materials.

In contrast, other options suggest delayed actions or conditions that may prolong the presence of danger on the highway, which goes against the principle of immediate accountability for maintaining a safe environment.