Critical Reasoning

There is only one major road, Freeway Z, that links County X and County Y. The border of the two counties is primarily defined by a mountain range, over which the construction of new roads is severely restricted by environmental laws. A cost-effective solution to the problem of traffic congestion on Freeway Z is to build a commuter train tunnel through the mountain range. The successful implementation of this plan would cost far less than expanding the existing freeway and would also reduce the number of cars clogging the roads in both counties.

Which of the following, if true, could proponents of the plan above most appropriately cite as a piece of evidence for the soundness of their plan?

A. An effective commuter train tunnel between the counties would require major investment in mass transit within both counties.
B. The majority of all vehicles on the nation's freeways are traveling from one state to another.
C. 60% of the cars on Freeway Z are driven by people who live in County Y and work in County X.
D. Many new freeways are being built in areas that are presently served by commuter trains.
E. A large proportion of the vehicles on Freeway Z are commercial trucks carrying transcontinental shipments.

I was able to shortlist to B and C but can't distinguish which one is better? Please help.

We are trying to evaluate the success of this plan -

A plan to build a commuter(people who travel to work regularly) rail system through the mountain range.

A - Weakens the argument. If the plan requires major investments in both counties, the probably it might not be cost-effective.

B - Not relevant. We are discussing two counties - X and Y. Also, we are discussing only about freeway Z. What happens on other freeways is not of concern.

C - correct answer. If the majority of cars driven on Freeway Z are for commuting to work, probably the new commuter railway system will reduce traffic congestion and be successful.

D - Not relevant. The argument is concerned only with Freeway Z.

E - weakens the argument. If a large proportion of vehicles of freeway Z are commercial trucks, then a commuter rail system will do little to ease the traffic congestion on Freeway Z.

I have a different observation regarding incorrect options:

Option A. The premise says it's a cost effective solution..

I think option A is against the premise.

If option A were to say:

An effective commuter train tunnel between the counties wouldn't require major investment in mass transit within both counties.

In this case it's a fact already mentioned in the premise.

B. Is generalising .. we want something specific.

D. Sort of weakner ..

E. Again a weakner....