918 - Logical Reasoning

Question: After the national speed limit of 55 miles per hour was imposed in 1974, the number of deaths per mile driven on a highway fell abruptly as a result. Since then, however, the average speed of vehicles on highways has risen, but the number of deaths per mile driven on a highway has continued to fall.
Which of the following conclusions can be properly drawn from the statements above?

1. The speed limit alone is probably not responsible for the continued reduction in highway deaths in the years after 1974.
2. People have been driving less since 1974.
3. Driver-education courses have been more effective since 1974 in teaching drivers to drive safely.
4. In recent years highway patrols have been less effective in catching drivers who speed.
5. The change in the speed limit cannot be responsible for the abrupt decline in highway deaths in 1974.