Refer to the Figure

question 8

Multiple Choice

Refer to the figure.
Vredenburg studied the impact of introduction of rainbow and brook trout on a species of amphibian, the mountain yellow-legged frog (Rana muscosa) . After showing greatly decreased frog populations in lakes with trout, he set up an experiment using three categories of lakes: lakes from which he removed trout, lakes that had never had trout, and lakes that still contained trout. He compared the number of adult frogs per 10 m of shoreline in all groups, as shown in the figure. In Vredenburg's experimental design, why did he use two control groups?

• A) To be doubly sure his results were correct
• B) To ensure that he had enough data for statistical analysis
• C) To control for unknown factors that might be present in the lakes
• D) To control for the effects of two known natural conditions

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Nine-Digit

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