Critical Reasoning

option c

C

Firstly, let us break the argument down into its constituent premises and conclusion.

Premise 1: The Monday following the Fourth of July weekend, Rosco Lake had twice as much trash in the streets and parks as usual
Premise 2: Rosco Lake is a popular tourist destination
Premise 3: Tourists visited the downtown Rosco Lake on the weekend

Conclusion: Tourists are responsible for the littering.

Now, we have to weaken the inherent causal connection between the tourists (cause) and littering (effect) in the above argument. The three main ways to weaken an X->Y cause-effect relationship on the GMAT are as follows:

• Z->Y - This option suggests that something else - an alternative factor Z - caused Y
  Y->X - This option reverses the direction of the cause-effect relationship - in other words, it suggests that Y causes X
  !X->Y - This option essentially suggests that the relationship between X and Y is purely coincidental, and even when the cause is absent, the effect can still be observed

Now, let us go through the given options -

Option A - Usually community volunteers go through downtown on Monday mornings, picking up litter - While this is surely one of the more nobler things a community member can do, it still doesn't answer our question of who/what caused the littering. Was it the tourists or the community members or someone else? - Incorrect
Option B - There is a correlation between tourist traffic and incidents of vandalism in many towns. - So it might very well be the case that the tourists were responsible for the littering in the downtown Rosco Lake. This is the opposite of what we want. Incorrect
Option C - During the other weekends in July, there were no unusual amounts of litter - Aha! This option says that the amount of litter collected was normal on weekends apart from the Fourth of July weekend. However, the tourists would presumably have visited Rosco Lake on other weekends, since it is a popular tourist destination. This option encapsulates the third way via which we can weaken a cause-effect relationship - even when the cause (the tourist) is present, the effect (excessive littering) is not there. This is a strong contender
Option D - The North Shore lakefront area in Rosco Lake is rarely visited by tourists, and has almost no litter, compared to the South Shore, which is a touristy area, and has lots of rubbish lying around - This would suggest a direct correlation between tourists and litter Incorrect
Option E - The nearby town of Graylord was able to control its litter problem by instituting large fines that could be levied against litterers.
- Out of scope; how nearby towns control their litter problems is beyond the argument Incorrect

This leaves us with Option C as our best answer, which essentially suggests that there is no correlation between the tourists visiting the Rosco Lake on the Fourth of July weekend and the excessive littering observed the following Monday.

Please let me know if anything doesn't make sense.