Self-study
Biologists found that off the northeast coast of a certain country the P-plankton population has recently dropped 10 percent. █████████████ ████ ███████ ██ ██ ███ █ ███ █████████ ██ ████ ███████████████ ████ █████ █████ ██ ███ ███████ █████ █████ ███████ ██ ████ ███ █████ ██ █████████ ███ ███████████ ██████████ ███████ ███ ███ █████████ ███ ██████████ ███ ███ █████ ██████ ██ ███ ██████████ ██ ████████ ██ █████ ███████ ██ ███ █████████ ██████ ██ ██ █████████
The Mystery
Three things are happening off the northeast coast:
1. P-plankton population dropped 10%.
2. Fish species X, Y, and Z are dying at unusually high rates.
3. No other species in the ecosystem appear to be affected.
The biologists think #1 and #2 are connected, but they don't know how. The fish are known to sometimes eat P-plankton, which is probably why the biologists suspect a connection, but notice that the stimulus doesn't commit to a specific direction of causation. Maybe whatever's hurting the plankton is also hurting the fish. Maybe the fish dying is somehow causing the plankton decline. Maybe something else entirely is causing both.
What Would Explain This?
For Resolve/Reconcile/Explain questions, we want to identify what's surprising and then look for an answer that makes it less surprising.
Here, the surprising thing isn't just that plankton and fish populations are declining. Populations decline all the time. What's surprising is the specificity: only P-plankton, and only fish species X, Y, and Z. If something broad like pollution or climate change were responsible, you'd expect other species to be affected too. But no other species are affected.
So the correct answer needs to thread a needle. It has to explain something that would harm P-plankton and fish X, Y, and Z, but not the rest of the ecosystem. Any answer that's too broad (harms everything) or too narrow (only explains one of the two phenomena) won't work.
23.
Which one of the following, ██ █████ ████ █████ ██ ███████ ███ ███████████ █████████
a
Several major pharmaceutical █████████ ██ ███ ██████ ████ ████ ████████ ███████ █████ ███████ ██ █████ ████ ███ █████ ███ ████ ██████
Two problems. First, the dumping has been going on for "many years," but the findings are recent. If companies have been dumping waste for years, why would the population declines only show up now? Second, pharmaceutical waste dumped into the ocean wouldn't selectively target P-plankton and three fish species. We'd expect other species in the ecosystem to be affected, too. But the stimulus tells us no other species appear to be affected.
b
A new strain ██ ████████ ██ █████████ ██████████ ██ ██████████ █████ ████ █████ ███ ██ █████████ ███ ███████████ ███████ ██ ████ ███████ ██ ██ ███ ██
This is the best answer. The bacteria destroys P-plankton cell walls, which accounts for the plankton decline. It attacks the respiratory systems of fish X, Y, and Z, which accounts for their high death rates. And because it's a new strain, this explains why the declines are recent. Most importantly, the bacteria is specific in what it targets: P-plankton and the respiratory systems of fish X, Y, and Z. There's nothing in (B) that suggests the bacteria would harm other species, which is consistent with no other species being affected.
c
A powerful toxin ██ ███ █████ ██ ███████ ███ ██████████ ██ ██████████ █████ ██████████ ██ █ ████████ ████ ███ ██ █████████████
This explains the P-plankton decline (a toxin is killing them), but it says nothing about what's causing the high death rates for fish X, Y, and Z. You might think, "Well, if P-plankton are dying, the fish lose a food source, so they die too." But the stimulus says the fish only sometimes eat P-plankton, and a 10% drop in plankton population doesn't obviously translate to "extraordinarily high death rates" for three fish species. (C) leaves half the mystery unsolved.
d
Fish species X, ██ ███ █ ███ ███ ████████████ ██████████ ██████████ ██████ ███ ████████ ███████ ███ ███ ████ ██ ██████████ ██ ███████ █████ █████ █████ ██ ████ ███████
This is tempting because it seems to connect the two phenomena: the fish are starving, and the loss of P-plankton is making things worse. But(D) says the fish are experiencing "widespread starvation," and that the loss of P-plankton is driving their death rates "even higher." This means the fish were already dying from starvation before the P-plankton decline made things worse. So (D) doesn't explain why the fish are starving in the first place. It also doesn't explain what caused the P-plankton population to drop.
e
Global warming has ███████ ███ ████████ ██████████ ██ ███ █████ ███ █████ ███ █████████ █████ ██ ███ ████████
Same core problem as (A). Climate change affecting the ocean "all along the northeast coast" is a broad, ecosystem-wide force. If global warming changed climatic conditions across the entire coast, we'd expect many species to be affected, not just P-plankton and three fish species. The stimulus is specific that no other species appear to be affected, and (E) gives us no reason to think global warming would be so selective.