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Here's an explanation for Question 5.
5. The views put forward in the passage conform most closely to which one of the following principles governing new methods of food production?(A) They should be employed only if they do not result in major changes in consumer demand for foods produced using traditional methods.This choice is incorrect because, if anything, it's basically the opposite of what the passage suggests.
The passage indicates that one of the issues with fish farming is that it does NOT necessarily cause reductions, i.e., changes, in demand for wild-caught fish, i.e. food "produced using traditional methods."
Here's the portion of the passage in the last paragraph that indicates that:
even these benefits may in the end be lost because niche markets have started to develop for several species of wild-caught fish, causing their catch rates to remain high even as the production of viable farmed substitutes has increased
Eliminate.
(B) They should be employed if they are economically more efficient than existing methods and their use will not result in business failures or loss of jobs.The passage does not advocate for "economically more efficient" methods of food production.
Also, "They should be employed if ... their use will not result in business failures or loss of jobs," conflicts with what the passage says in that the passage suggests that "reducing fishing efforts," in other words, a decline in fishing business, would be beneficial.
Eliminate.
(C) They should not be employed if they will ultimately result in a net decrease in food of the type produced.This choice may not perfectly match the passage, but it works pretty well.
The passage says the following:
fish farming is a possible solution, but also a potential contributing factor, to the continued decline of ocean fishery stocks worldwide
Habitat destruction through the spread of untreated waste, the escape of species not native to the farm's region, or contamination by new pathogens can all ensue, seriously damaging ... wild fishery stocks.
Although some defenders of fish fanning contend that predatory carnivores in the wild consume even more fish than they would on a farm, farming of such carnivorous species requires up to 5 kilograms of wild fish for every kilogram of fish produced.
Those statements, along with others in the passage, make sense in the context of the principle that, if fish farming causes "decline of ocean fishery stocks," then fish farming should not be engaged in. In other words, the author's discussion assumes that principle as a given.
That principle is a specific example of the more general principle "new methods of food production" "should not be employed if they will ultimately result in a net decrease in food of the type produced."
Keep.
(D) They should be employed if they promote diversification in the types of foods available for human consumption and help to bring about environmental improvement.This choice is tempting because it has the vibe of fitting what the passage says since the passage is about "foods available for human consumption" and since it mentions environmental effects of fish farms.
However, this choice is incorrect because the passage does not advocate for use of methods that "promote diversification in the types of foods available." Rather, it says that fish farms may be beneficial if they "alleviate some of the pressure on wild fishery stocks."
Also, regarding "environmental" effects, the passage mentions only the negative environmental effects of fish farming such as "habitat destruction," the benefits it focuses on once again being related to restoring "fishery stocks," rather than related to the environment in general.
Eliminate.
(E) They should be employed only if they replace other methods that have undesirable ecological effects.This choice is tempting because the passage does indicate that replacing fishing for wild fish with fish farming could result in a reduction in some "undesirable" effects.
However, the passage does not ever suggest that methods should be used "only if" they replace methods that have undesirable ecological effects.
There's a difference between suggesting that some methods are ecologically better than others and suggesting that methods should be used only if they "replace" methods that have undesirable ecological effects.
In other words, the passage never suggests that methods should not be used if they don't replace methods that have undesirable ecological effects.
Eliminate.
The correct answer is (C).