Of the four major cities in a region, City A, City B and City C all lie on the shore of Lake X. City D, however, lies on

Of the four major cities in a region, City A, City B and City C all lie on the shore of Lake X. City D, however, lies on the shore of Lake Z. All four cities use the lakes that they lie on to dump treated sewage and the citizens of all four cities also use the lakes for recreation. A scientist theorized that Lake Z, next to City D, would be cleaner than Lake X because, from the perspective of Cities A, B, and C, each would accrue all the benefits of dumping sewage in Lake X, but would spread the costs of having the sewage in the lake across the three cities. At the same time, City D would have to deal with all the costs of having the sewage in Lake Z, so the scientist concluded that City D would dump less sewage. After surveying the two lakes, however, the scientist found that the opposite was true – there was more sewage in Lake Z.

Each of the following, if true, would help explain the results found by the scientist, EXCEPT:

A. Two years ago, Cities A, B and C spent a considerable sum on a sewage clean-up project in the lake next to their cities

B. No monitoring systems exist that can tell exactly how much sewage is being dumped by each of the four cities

C. Cities A, B, and C all know that if one of the cities overuses the lake for sewage dumping, the other two will dump even more sewage, with the consequence that the lake would be completely ruined for recreational use

D. City D has been dumping sewage in Lake Z for 175 years, while the other three cities have only used Lake X for dumping for 25 years each

E. City D is twice the size of the other three cities combined

OA B