@JayDee8732 the problem with (B) is that it does not address the discrepancy here.
The discrepancy here is that widening and extending highways in an attempt to reduce traffic congestion and resulting delays actually increases traffic and delays.
Notice (A) serves as a possible explanation for this discrepancy.
The reason why widening and extending highways actually increases traffic congestion and delays is because these widened and extended roads tend to attract many more motorists than used them before they were improved.
Hope that helps! Please let us know if you have any other questions.
