SAT OwlQuestion bank / Command of Evidence
Since 2000, the population of lake trout in Ellery Lake has fallen by nearly half. Biologist Hana Sato attributes the decline mainly to rising summer water temperatures, which shrink the layer of cold, oxygen-rich water that lake trout need. Other researchers point instead to zebra mussels, an invasive species first detected in the lake in 2003, which filter out the plankton at the base of the lake's food web.
Which finding, if true, would most directly support Sato's explanation over the alternative explanation?
Zebra mussels have spread to many other lakes in the region since 2003.
Lake trout populations have fallen by similar amounts in several nearby lakes that have warmed as much as Ellery Lake but contain no zebra mussels.
The amount of plankton in Ellery Lake has declined since zebra mussels were first detected there.
Lake trout need colder water than most other fish species found in Ellery Lake.
Show answer and explanation
Answer: B
To favor Sato's view, a finding must separate warming from mussels. Choice B describes lakes with the same warming but no zebra mussels, and trout declined there too. That suggests warming alone can produce the decline, which supports Sato over the mussel explanation.
Choice D fits Sato's reasoning, but it is true whether or not warming caused the decline, so it does not help decide between the two explanations.
Why the other choices are wrong
- A. This finding shows mussels are widespread but does not link them to the trout decline in Ellery Lake. It fails to separate the effects of warming from the effects of mussels.
- C. This supports the alternative explanation by confirming mussels reduce plankton. It does not show that warming is the primary cause of the population decline.
- D. This is a general fact about trout biology that remains true regardless of the cause. It does not distinguish between warming and mussels as the driver of the decline.
Got it wrong? On SAT Owl, Owl looks at the answer you chose and explains the exact mistake, then gives you similar questions until it sticks. Get your predicted SAT score free, or take a free full-length practice test.