The given passage is having a argument to not support helmet law.
Now, this question says,
Which of the following, if true, most weaken the argument above?
while,
option C says , The rate of accidents in states with mandatory helmet laws is lower than in states with no laws.
- it deals with support for helmet law. which is opposite with the essence of the passage.
But that option B deals with Insurance rates, which have no connection with the argument of the passage.
Same for option A and option D, these two also have no relation with given argument in passage .