Question 139·Easy·Inferences
Biologist Emily Sung studied a population of frogs in a remote wetland. She observed that in years with higher rainfall, the frogs laid twice as many eggs, and the survival rate of tadpoles increased markedly. Sung also notes that lower rainfall years coincide with a noticeable decline in the wetland’s insect population.
Based on Sung’s observations, it can reasonably be inferred that the frogs’ reproductive success is closely linked to ______
Which choice most logically completes the text?
For SAT inference completion questions, first identify the key pattern or cause-and-effect relationship described in the passage, then look for the answer choice that restates or logically extends that pattern without adding new, unsupported ideas. Pay close attention to what the passage actually mentions (here, rainfall, egg-laying, tadpole survival, and insects) and quickly eliminate any choices that introduce completely new factors (like genes, predators, or competition) that were never brought up.
Hints
Locate the key cause-and-effect details
Reread the sentences that describe what happens in years with higher rainfall and what is observed in years with lower rainfall. What changes in each case?
Connect the two observations
Ask yourself: How might the change that happens in low rainfall years (mentioned at the end) explain why frog reproductive success is different from high rainfall years?
Check for outside ideas
Look for whether the passage ever mentions genetic changes, competition with other amphibians, or new predators. If an option introduces something that never appears in the passage, treat it with suspicion.
Step-by-step Explanation
Restate what the question is asking
The question asks what the frogs’ reproductive success is closely linked to. That means you must identify what factor, based on Sung’s observations, seems most directly connected to how many eggs are laid and how many tadpoles survive.
Pull out the key observations from the passage
The passage gives two important observations:
- In years with higher rainfall, the frogs laid twice as many eggs, and tadpole survival increased.
- Lower rainfall years coincide with a noticeable decline in the wetland’s insect population.
So, higher rainfall is associated with better frog reproduction and survival, while lower rainfall is associated with fewer insects.
Infer the hidden connection
The passage does not explicitly say what connects rainfall to frog reproductive success, but it hints at it. Rainfall seems to affect the insect population, and insects are a likely food source for frogs and/or tadpoles. More insects probably mean more food, which can support more eggs and better survival. So, the factor that really matters for reproductive success is the one that changes with rainfall and is directly useful to frogs.
Match this inferred factor to the answer choices
Now compare this idea to the options:
- Nothing in the passage mentions genetic changes, competition with other amphibians, or predators moving in.
- The passage does highlight that insect numbers drop when rainfall is low, at the same time frog success is lower.
The only answer that reflects this logical connection is D) the availability of insects in the wetland.