Could someone plz explain the correct answer?

Let's start with why the argument is bad. The author thinks that we should raise speed limits, because the data shows that fatalities are actually rising in areas with low speed limits. Does this make sense to you? I would attack this by asking about areas with high speed limits. What if those areas are increasing at the same rate, or even higher? Even if this is not the case, a slight increase in the rate of fatalities for low speed limit places might takes decades to catch up with high speed limit areas. Regardless, the first objection is a perfect match for D. We have no idea about the areas where speed limits are high. If the rate of fatalities are increasing there as well, then the authors argument makes no sense.