Re: When so many oysters died off the coast of Britain that some native sp
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26 Nov 2023, 16:07
Explanation
When so many oysters died off the coast of Britain that some native species were threatened with extinction, the fact that the water temperature had recently risen was at first thought to be the cause. Later, however, the cause was determined to be the chemical tributyl tin (TBT), used to keep barnacles off the hulls of boats. Legislation that banned TBT has nearly eliminated that chemical from British waters, yet the populations of the endangered oyster species have not grown.
We are presented with a scenario in which native species of oysters were threatened with extinction and the cause of the die off was determined to be the chemical tributyl tin (TBT), but even though TBT has been nearly eliminated, the populations of the endangered oyster species have not grown.
Which one of the following, if true, most helps to explain the failure of the native oyster populations to recover?
The correct answer will explain why the oyster populations haven't recovered even though the cause of the decline has been eliminated.
(A) The increase in water temperature has slowed in the years since the legislation was passed.
This choice is incorrect for two reasons.
One is that the information in the passage indicates that the increase in the water temperature did NOT cause the population decline.
The second is that the fact that the increase in water temperature slowed means that the situation changed more slowly. A decrease in the rate of a change in the situation would not be the reason for the development of a new issue such as that the populations didn't recover even though TBT was eliminated.
Eliminate.
(B) Native oysters rely on different sources of food than do the barnacles that live on the hulls of boats.
The passage does not mention lack of food as the cause of the death of oysters, or barnacles. What's mentioned as a cause of the death of both is TBT.
So, we can eliminate this choice as off topic.
Eliminate.
(C) TBT also killed imported varieties of oysters that flourish at the expense of native oysters now that the waters are warmer.
To see why this choice explains the mystery of why the populations haven't recovered, we need to identify the factors at play and make common-sense, logical connections.
What we can see is that, if TBT killed imported varieties of oysters that flourish at the expense of native oysters now that the waters are warmer, then with the elimination of TBT, those imported varieties of oysters can now flourish. As a result, with the elimination of one cause of the native oyster population decline, TBT, another cause of native oyster population problems came into play that offset the elimination of TBT, imported oysters.
The fact that such an offset occurred perfectly explains why, even though TBT has been nearly eliminated, the native oyster populations haven't recovered.
A key takeaway from this choice is that, to get CR questions correct, we need to read choices in their entirety. After all, if we focus on just the first part of this choice, "TBT also killed imported varieties of oysters," we could easily decide that this choice is an irrelevant statement about oysters other than the ones we're concerned with.
Keep.
(D) Other chemicals that are used to remove barnacles from the hulls of boats seem to have little effect on the oyster populations.
This choice eliminates an alternative cause that could have kept the oyster populations from recovering, other chemicals still used that harm oysters.
So, this choice actually deepens the mystery of why the populations haven't recovered.
Eliminate.
(E) TBT is more deadly to oysters in colder waters than in warmer waters.
This choice is clearly out.
For one thing, TBT has been nearly eliminated. So, presumably, TBT isn't a factor at this point.
Furthermore, the passage indicates that the waters have become warmer. So, according to this choice, TBT should be less deadly than before.
A key thing to notice about this choice is how it mentions two things from the passage, warmer waters and TBT, to give the vibe of having something to do with the mystery we need to explain and thus tempt us to choose it.
Eliminate.
The correct answer is (C).