Question 47·Medium·Central Ideas and Details
Over the past five years, ecologists at the University of Aberdeen have monitored beavers reintroduced to the River Forth in Scotland. The animals have built more than forty dams, slowing the river’s flow and trapping sediment. Measurements show that the water downstream now contains 30% fewer agricultural pollutants than before the dams were constructed. The researchers believe this filtration benefit outweighs the occasional farmland flooding reported by local residents.
According to the passage, what effect have the beaver dams had on the water downstream of the river?
For detail questions that ask “According to the passage…,” go back and find the exact sentence that addresses what the question is asking (here, the effect on water downstream). Underline or mentally note the key words that changed (for example, “30% fewer agricultural pollutants”), then restate them in your own words. Finally, pick the answer that most closely paraphrases that specific line and eliminate any options that bring in new ideas or details not mentioned in the passage.
Hints
Focus on the evidence in the passage
Reread the part of the passage that begins with “Measurements show that the water downstream now contains…” and think about what changed in the water.
Identify what is being measured
Ask yourself: what exactly did the ecologists measure in the downstream water, and did it increase or decrease?
Eliminate unrelated changes
Check each answer choice and cross out any that mention effects the passage never talks about, such as changes in temperature, fish populations, or the river’s path.
Step-by-step Explanation
Locate the sentence that describes the effect
Look back at the passage and find where it specifically talks about what changed in the water downstream after the beavers built dams. This is in the sentence: “Measurements show that the water downstream now contains 30% fewer agricultural pollutants than before the dams were constructed.”
Restate that effect in your own words
Put that sentence into simpler terms: the water downstream now has less agricultural pollution than it had before. The key idea is a reduction in agricultural pollutants in the downstream water.
Match the paraphrase to the answer choice
Now compare that idea (less agricultural pollution downstream) to the answer options. The only choice that matches this stated effect is: “The dams reduced the concentration of agricultural pollutants in the water.”