Case 1: fatalities have reduced significantly since the introduction of speeding limits
Case 2: proportion of drivers who were driving their vehicles at high speeds is not lower than that before 2005
We need an event that allows both of the event to occur.
A. The proportion of cars being driven on the roads post 2005 is not the same as prior to 2005.
Out of topic; proportion of cars on the roads? what are other cars doing?)
B. The proportion of people using seat belts and air-bags, proven to be effective safety measures, has increased significantly post 2004.
Even though number of speeding drivers has not decreased, they are wearing seatbelts and using airbags, reducing the number of fatalities.
Accommodates both situations.
Therefore, correct answer
C. Speeding is higher among the younger set of drivers than among the older, more cautious ones.
Irrelevant. Why fatalities decreased?
D. Most people find it very hard to give up their old habits of speeding even when faced with regulations restraining them from it.
Explains speeding,
but not decreased fatalities.
E. The number of miles driven per car on average is no lower than it was prior to 2005.
Irrelevant. Why fatalities decreased, and why speeding is still a problem?