Question 157·Easy·Inferences
Environmental scientist Dr. Leong analyzed water samples from Lake Orion after a nearby manufacturing plant installed a new filtration system. Within six months, heavy-metal concentrations in the lake had dropped by nearly 40 percent, while measurements at upstream sites remained unchanged. Based on these observations, it can most reasonably be inferred that the manufacturing plant ______
Which choice most logically completes the text?
For SAT inference-completion questions, first restate the key facts in your own words, especially changes over time or contrasts like upstream vs. downstream. Then ask, “What conclusion is most reasonable based only on these facts?” Eliminate any answer choices that introduce new details (like motives, future events, or specific policies) that are not mentioned in the passage, and choose the option that directly reflects the pattern or relationship described.
Hints
Focus on what changed and what didn’t
Notice what happened after the manufacturing plant installed the new filtration system, and also what happened to the upstream measurements during the same time.
Think about cause and effect
Ask yourself: if one part of the water system shows a big change, but another part (upstream) does not, what does that suggest about where the problem was coming from?
Watch out for extra information
Eliminate choices that talk about things the passage never mentions, such as the plant’s future business decisions, reasons for installing the system, or government actions.
Step-by-step Explanation
Restate the important facts from the passage
First, summarize the key information:
- A nearby manufacturing plant installed a new filtration system.
- Within six months, heavy-metal concentrations in Lake Orion dropped by nearly 40 percent.
- Measurements at upstream sites (locations before the lake, higher in the river/stream) stayed the same.
These are the clues you must use to make a logical inference.
Understand the significance of upstream vs. the lake
Upstream sites are locations before the water reaches Lake Orion and the plant.
- If upstream heavy-metal levels did not change, that means the source of metals upstream stayed the same.
- But in the lake, levels did drop a lot after the plant installed filtration.
So something that affects only the lake, not upstream, must have changed.
Connect the timing of the filtration system and the drop in metals
The big event that changed was the manufacturing plant installing a filtration system.
- Right after this change, heavy-metal levels in the lake dropped sharply.
- Nothing upstream changed (the measurements remained steady).
This makes it very reasonable to link the plant's wastewater (before filtration) to the high heavy-metal levels in Lake Orion.
Compare each answer choice to the evidence and choose the best one
Now test each answer against the passage:
- Choice A: Talks about increasing production because water quality improved. The passage doesn’t mention production levels or the plant’s plans.
- Choice B: Says the plant acted “due solely to community pressure.” The passage gives no information about why the plant installed filtration.
- Choice D: Predicts the plant “will soon close” because of “stricter environmental regulations.” The passage never mentions closures or new regulations.
Only Choice C, “was the primary source of heavy-metal contamination in Lake Orion,” matches the observed pattern: once the plant started filtering, the lake’s heavy-metal levels dropped, while upstream stayed the same, indicating the plant had been the main contributor to the lake’s heavy-metal contamination.