Let us simplify the argument --
Traffic in East Countyway has gotten worse after opening Tricounty Bridge --> To relive traffic, Tricounty Bridge should be closed.this is not a very strong argument. What if the traffic increased because of some other reason? Closing the bridge then would worsen the situation even more.
Let us take a look at other answer options --
Option A - IncorrectThis provides an alternate reason for the increase in traffic in East Countyway. Closing the bridge would then not have much impact on the traffic in East Countyway. (What if people who came to the casino and resort hotel did not use the bridge at all? then traffic due to the casino would not decrease)
Option B - Correct answerNote that this option states that West Countyway is "heavily populated". If people from there can reach East Countyway in 1/4th the time, it means that theoretically 4 times as many people can come to East Countyway in the same amount of time.
Closing the bridge then would decrease this the rate of influx.
Option C - IncorrectIf the bridge is open for such short durations, it is then probably not responsible for the increase in traffic. Closing the bridge would then do little to ease the traffic situation.
Option D - IncorrectThis does not affect the conclusion at all -- "
To relive traffic, Tricounty Bridge should be closed."
Option E - IncorrectThis does not affect the conclusion at all -- "
To relive traffic, Tricounty Bridge should be closed."