Question 73·Easy·Inferences
Biologist Dana Lee compared the mating calls of the same frog species in urban ponds and remote forests. She found that male frogs in urban ponds consistently produced calls about 300 hertz higher than those in forests. Lee noted that the urban ponds sat beside busy highways whose engine and tire noise peaks below 500 hertz, whereas the forests were nearly silent at night. Based on Lee’s findings, the change in call pitch among urban frogs is most likely ______
Which choice most logically completes the text?
For “most logically completes the text” questions, first identify the key relationship or contrast in the passage (here, different call pitches in noisy vs. quiet habitats and the specific noise frequency). Ask what cause or purpose best explains that pattern, then test each choice against the passage: eliminate answers that introduce new topics not mentioned (like reproduction rates), contradict the data (like random error in a consistent finding), or make stronger claims than the text supports (like saying a group is incapable). Choose the option that directly connects to the given details and offers a reasonable, supported inference.
Hints
Focus on the contrast between locations
Look back at how the calls of frogs in urban ponds differ from those in remote forests, and how the two environments themselves differ in sound.
Use the frequency information
Pay attention to the detail that traffic noise "peaks below 500 hertz" while the frogs’ urban calls are "about 300 hertz higher" than forest calls. How might this relationship matter for communication?
Check for outside information in choices
Ask yourself which choices bring in ideas that are not mentioned in the passage (for example, about reproduction rates or equipment problems) and which one is directly supported by the described pattern.
Step-by-step Explanation
Restate the key facts from the passage
First, summarize what the passage tells you:
- The same species of frogs lives in two environments: urban ponds and remote forests.
- Male frogs in urban ponds make calls about 300 hertz higher than those in forests.
- Urban ponds are next to busy highways, where engine and tire noise peaks below 500 hertz.
- The forests are nearly silent at night. These details clearly contrast noisy urban ponds with quiet forests and link that to a systematic change in call pitch.
Infer the relationship between call pitch and background noise
Ask: Why would frogs in noisy urban ponds have higher-pitched calls than frogs in quiet forests?
- Highway noise "peaks below 500 hertz," meaning most of its sound energy is in lower frequencies.
- If frogs raise their call pitch above much of that noise, their calls will be easier to hear over the background traffic.
- Because this pattern is consistent (not occasional), it suggests a systematic difference tied to the environment, not a one-time accident.
Match the logical inference to the answer choices
Now check each answer against the evidence and the logical inference that frogs in noisy environments benefit from calls that stand out from traffic noise:
- Eliminate choices that talk about equipment errors or new facts (like reproduction rates or forest frogs’ physical limits) that are never mentioned.
- The best choice will explain the consistent higher pitch in noisy urban ponds, using the idea that traits can change over time to improve survival or mating success.
- The only option that fits the evidence and this reasoning is “an evolutionary response that helps the frogs be heard over traffic noise.”