Hello there!
For this question, I think the most important words/idea that should be noticed are, "straight, level road at at constant velocity."
The question, "Which forces form an action/reaction force pair?" will tell you that you are looking for an answer that gives a logical reason behind a force that is being used.
With that being said, I would skim over these answers and see which of the group are the LEAST logical.
The answers B, and D, though they might sound convincing, are incorrect.
Once again, remember the keywords, "straight, level road at a constant velocity."
This tells us that there is no angel and/or steep hill that the car is driving over or on; it also tells us there are no factors that the car is pulling or forcing anything with it.
Answer choice A: This answer shows us the "force of the tires against the road and the force of the road on the tires." This could be hinting at the FRICTION. (a force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other) and/or the tires are showing a "pulling force," while the road is acquiring a, "pushing force," due to the external action/force being brought upon it.
Answer choice C: This answer applies that the engine is creating something called a, "pull force," and while this is a force you could be looking for, remember that the car is at a, "constant velocity." meaning that if there are no angles, or steep hills, there is no reason to accelerate and cause the pull force to come into play.
Therefore; I would say A is the most logical, and reasonable answer.
I hoped this helped! Have a great day :)