Biologists tracked four lakes over five years, measuring fish populations and recording two factors: presence of an invasive species (yes/no) and average water temperature change (°C). Lake A: invasive yes, +0.5°C, fish drop 40%; Lake B: invasive no, +0.5°C, fish drop 5%; Lake C: invasive yes, +0.0°C, fish drop 35%; Lake D: invasive no, +0.0°C, fish drop 2%. The researchers concluded that invasive species presence, not temperature change, was the primary driver of the fish decline. The strongest data support for this specific causal claim is ______
Which choice most logically completes the text using the data above?
- A
the comparison between Lake C (35%) and Lake D (2%), since both had no temperature change.
- Bcheck_circle
both B and C are correct, since each holds one variable constant while varying the other.
- C
the comparison between Lake A and Lake B—both with the same +0.5°C, but A (invasive) lost 40% while B (no invasive) lost only 5%.
- D
the comparison between Lake A (40% drop) and Lake D (2% drop).
Explanation
To establish that invasives—not temperature—drive the decline, you need data that holds one factor constant while varying the other, in BOTH directions. Comparison B-vs-A holds temperature constant; comparison D-vs-C holds temperature constant at zero. Both pairs show that invasives matter independent of temperature. Either alone is good; together they're stronger, so D is the best answer.