medium · GRE Verbal
European eel populations have collapsed by more than ninety percent since the 1970s. **Commercial overfishing of juvenile eels is commonly blamed for the collapse**, and export records do show heavy harvests during the 1980s. However, populations have continued to fall even in rivers where eel fishing has been banned for decades, and the steepest declines coincide with the construction of hydroelectric dams along major migration routes. Tagging studies find that fewer than half of migrating adults survive passage through a single dam's turbines. **The chief driver of the collapse is more likely the fragmentation of migration routes than the harvest itself.**
In the argument above, the two portions in boldface play which of the following roles?
- The first is a finding that the argument accepts as accurate; the second is an explanation that the finding contradicts.
- The first is an explanation that the argument challenges; the second is the rival explanation that the argument favors.
- The first is the main conclusion of the argument; the second is an alternative account that the argument ultimately rejects.
- The first is evidence offered for the argument's conclusion; the second is the conclusion that the evidence supports.
- The first is an explanation that the argument challenges; the second is evidence offered against that explanation.
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