Concept:The correct phrasal verb is "run over", which means a vehicle hits and passes over a person or animal.
Explanation:The sentence needs a word that combines with "run" to describe a careless driver hitting the dog with a car.
The standard expression in English is "run over".
For example: "The dog was run over by a careless driver."
Option A, "under", does not form a common phrasal verb with "run" in this sense.
Option B, "upon", is old-fashioned and not used for vehicle accidents.
Option C, "across", changes the meaning to "meet by chance", which is not appropriate here.
Therefore, the only correct choice is "over".
Answer:D. over