The correct answer is (D).
Restoring Europe's Farmland
Step 1: Read the Passage Strategically
Sample Highlighting
As part of an international effort to address environmental problems resulting from agricultural overproduction, hundreds of thousands of acres of surplus farmland throughout Europe will be taken out of production in coming years. Restoring a natural balance of flora to this land will be difficult, however, because the nutrients in soil that has been in constant agricultural use are depleted. Moreover, much of this land has been heavily fertilized, and when such land is left unplanted, problem weeds like thistles often proliferate, preventing many native plants from establishing themselves. While the quickest way to restore heavily fertilized land is to remove and replace the topsoil, this is impractical on a large scale such as that of the European effort. And while it is generally believed that damaged ecological systems will restore themselves very gradually over time, a study underway in the Netherlands is investigating the possibility of artificially accelerating the processes through which nature slowly reestablishes plant diversity on previously farmed land.
In the study, a former cornfield was raked to get rid of cornstalks and weeds, then divided into 20 plots of roughly equal size. Control plots were replanted with corn or sown with nothing at all. The remaining plots were divided into two groups: plots in one group were sown with a mixture of native grasses and herbs; those in the other group received the same mixture of grasses and herbs together with clover and toadflax. After three years, thistles have been forced out of the plots where the broadest variety of species was sown and have also disappeared from mats of grass in the plots sown with fewer seed varieties. On the control plots that were left untouched, thistles have become dominant.
On some of the plots sown with seeds of native plant species, soil from nearby land that had been taken out of production 20 years earlier was scattered to see what effect introducing nematodes, fungi, and other beneficial microorganisms associated with later stages of natural soil development might have on the process of native plant repopulation. The seeds sown on these enriched plots have fared better than seeds sown on the unenriched plots, but still not as well as those growing naturally on the nearby land. Researchers have concluded that this is because fields farmed for many years are overrun with aggressive disease organisms, while, for example, beneficial mycorrhiza—fungi that live symbiotically on plant roots and strengthen them against the effects of disease organisms—are lacking. These preliminary results suggest that restoring natural plant diversity to overfarmed land hinges on restoring a natural balance of microorganisms in the soil. In other words, diversity underground fosters diversity aboveground. Researchers now believe that both kinds of diversity can be restored more quickly to damaged land if beneficial microorganisms are "sown" systematically into the soil along with a wide variety of native plant seeds.
Passage Notes
Paragraph 1
Restoring land damaged by farming is difficult
Will restore naturally, but study investigating how to accelerate process artificially
Paragraph 2
Study methods
Results
Paragraph 3
Adding beneficial microorg
Why microorg helpful
Planting seeds and "sowing" in microorg is key to boosting diversity.
Discussion
In paragraph 1, the author introduces the Topic: farmland in Europe; and quickly narrows to Scope: problems with overproduction of that land. One problem in particular captures the author's attention: How can we restore a natural balance of flora to land that has been overworked? The second and third sentences of paragraph 1 detail some difficulties in solving this problem: The land has been stripped of nutrients, highly fertilized, and overrun by thistles. The author then goes on to present a quick solution (removing and replacing the topsoil), but tells you that this solution isn't practical. By the end of the paragraph, the author mentions that a study is underway to determine whether humans can accelerate the process of reestablishing biodiversity on this land.
Paragraph 2 describes the study's methodology—a former cornfield was divided into identical plots, some control and some variable—and gives some initial results three years into the study. On control plots, thistles dominated. On plots where a diverse set of flora was sown, thistles disappeared.
Paragraph 3 continues to detail the results of the study. Some of the plots of land were enriched with beneficial microorganisms, and those plots better supported seedlings than did plots that were not enriched. The third sentence of paragraph 3 introduces an explanation for this: Land farmed for many years contains a lot of harmful organisms and not very many beneficial organisms. This explanation leads to the author's ultimate recommendation: The sowing of native plant seeds should be accompanied by the introduction of beneficial microorganisms into the soil. This recommendation reveals the author's Purpose: to lay out a strategy for restoring a natural balance to overworked farmland; and Main Idea: natural balance can be restored by introducing both native seeds and beneficial microorganisms to damaged land.
(D) Inference
Step 2: Identify the Question Type
Any question asking you to determine what is "most likely to be true" based on the passage is an Inference question. Despite this wording, know that you're seeking the answer that must be true.
Step 3: Research the Relevant Text
The stem directs you to the first paragraph, where the author discusses replacing topsoil as the quickest solution to restore heavily fertilized land (fourth sentence of paragraph 1).
Step 4: Make a Prediction
Some Inference questions, such as this one, can be reasonably predicted. If replacing topsoil is indeed a way to fix the problems associated with heavily fertilized land, then the soil used to replace the topsoil will probably not be heavily fertilized.
Step 5: Evaluate the Answer Choices
(D) is consistent with the prediction
(A) is Extreme. Nothing suggests that the new soil will be totally free of thistles—just that the thistles won't take over.
(B) is, if anything, a 180. Fungi are mentioned in paragraph 3 as beneficial to native plant diversity, so presumably, new topsoil would be helped by fungi.
(C) is unsupported because the topsoil is being replaced in order to remove the fertilizer and restore the nutrients. The number of seeds of native herbs and grasses already in this soil is unimportant.
(E) also doesn't need to be true. The replacement soil could have been used to grow any crop, as long as that soil is not heavily fertilized and/or depleted of nutrients.
