CR Question - Conclusion.

[ps63739]

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?
(A) The speed limit alone is probably not responsible for the continued reduction in highway deaths in the years after 1974.
(B) People have been driving less since 1974.
(C) Driver-education courses have been more effective since 1974 in teaching drivers to drive safely.
(D) In recent years highway patrols have been less effective in catching drivers who speed.
(E) The change in the speed limit cannot be responsible for the abrupt decline in highway deaths in 1974.

Correct Answer is A.
C and D eliminated easily. E can be eliminated since it strongly mentions speed limit cannot be responsible. (let me know if there is flaw in my understanding)
Now why can't B be taken as an answer? Or would that be an assumption? Since the speed limit has increased and no. of deaths per mile have gone down. That can draw an inference that people have started driving less.
Any suggestions?

[chunyang.yu]

from the passage, we can know that the speed limits has partly contributed to the decline, and other reasons must have facilitated the decline

but here, these other reasons can be what mentioned in option B, or something others whick can not be sure simply from the passage

[Ben Ku]

Please cite the source (author) of this problem. We cannot reply unless a source is cited (and, if no source is cited, we will have to delete the post!). Thanks.

[ps63739]

I was looking online for questions. Here is where I got the problem - http://www.beatthegmat.com/national-spe ... 18390.html

The answer was A.