Therefore, (D) is incorrect.
C Choice (A) is extreme; while the size of wolf packs is a limiting factor, there is no evidence
in the passage to suggest that it is the major limiting factor. And though the passage
discusses how wolves and other factors affect the elk population, it does not mention the
superior hunting tactics of wolves, so (B) is incorrect. Because the passage discusses the
effect of wolf populations and elk populations on one another, (C) accurately describes the
relationship between elk and wolf populations. Choice (D) is also extreme; while the size
of elk packs affects wolf populations, there is no evidence to suggest it is the major
limiting factor. Therefore, the correct answer is (C).
A The answer to the previous question is that the sizes of wolf and elk populations affect one
another. Choice (A) notes that wolf population numbers in YNP have declined mostly
because of a smaller elk population. Because wolves primarily prey on elk in YNP, their
population must affect the elk population; the explicit statement here that the smaller elk
population affected the number of wolves shows that the elk population also affects the
wolf population. Choice (B) discusses bison, so it is not relevant as evidence about the elk
and wolf populations. Choice (C) notes that wolf-prey relationships were studied does not
give any specific information about those relationships. Choice (D) offers support for the
claim that the wolf population affects the elk population but lacks support for the reverse
relationship. Thus, (B), (C), and (D) are incorrect, and (A) is the correct answer.
D The sentence states that weather affects the ability of elk to forage. This has nothing to do
with tracking wolves in Yellowstone. Therefore, (A) is incorrect. There is no evidence that
the quality of the food has improved, so (B) is incorrect. Choice (C) is also incorrect;
while the paragraph mentions predation studies, it does not argue for them. Because
weather patterns influence forage quality and availability and forage quality and
availability in turn affect the elk population, the reference to the weather does provide
additional information about a cause of the decline of elk in Yellowstone. Therefore, (D) is
correct.
A The graph shows that the wolf population in 2010–2011 was about 40, while the elk
population was about 4,500. The wolf population has never reached as many as 120 during
the time reflected in the graph, while the elk population had not dipped below the mid-
4,000s in 2011; therefore, the graph supports the claim that elk populations currently
outnumber wolf populations in YNP, and (A) is supported by the graph. Because elk
populations increased from 1998 to 2000 and in other years, (B) is incorrect. Elk
populations were at their lowest in 2010–2011, but wolf populations were at their highest
in 2003–2004, so (C) is incorrect. Because there are about 40 wolves and 4,500 elk in
Yellowstone as of 2011, (D) is incorrect. If you answered (D) or eliminated (A), you likely
did not notice that the wolf population is on the left axis of the graph and the elk population
is on the right.
C The question asks what the author suggests about mammals in the first paragraph of Passage
Choice (A) is incorrect because the paragraph states that more than half of all species
were wiped out in the KT extinction, so species other than mammals must also have