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Assumption. The correct answer choice is (A)
Assumptions are typically unspoken statements that the author must believe in order to believe that
argument. If the author’s belief in an assumption were rendered untenable, the argument would no
longer be believable. The argument here is that failure to preserve tropical rain forests will prevent
the development of important types of medicine. This belief is supported by evidence that many
types of medicine have come from substances only found in tropical rain forests and that many
similar substances in these rain forests remain undiscovered.
A further belief is required in order for the author to believe that important types of medicine would
go undiscovered if rain forests were destroyed. The author must believe that since past medicines
came in this manner, at least some future medicines could not come in any other way. Put differently,
if these medicines could be developed without discovering yet unknown substances in tropical
rain forests, then the author could not believe that preserving the rain forests was a necessary precondition
for the medicine’s development.
Answer choice (A): This is the correct answer choice. Discovery of unknown substances is
required for future development of medicine if our knowledge of current substances would not
lead to the same development. As with any Contender to an Assumption question, you can test this
answer by negating it and determining if it renders that argument unacceptable. This answer can be
negated as “there are no unknown substances of medicinal value that differ from substances already
discovered.” If the negation were true, then it would be unnecessary to preserve rain forests since
scientists could develop the same types of medicine by studying existing, known substances.
Answer choice (B): This answer would weaken the argument. If the author believed that most
substances from the rain forest were not unique to that environment, then it would be less necessary
to preserve the rainforest.
Answer choice (C): An assumption does not have to strengthen an argument. Many incorrect answers
on assumptions go beyond what is required for belief in the argument.
Here, for example, we are told that the majority of unique plant species contain substances of medicinal
value. Since there are so many unique plant species in the rain forest and most of them are likely to
have medicinal value, this would certainly support the importance of preserving the rain forest.
But that’s not the author’s argument; the author is arguing that developing important medicines
depends on preserving the rain forest. In order to believe that conclusion, the author does not have to
believe that the majority of plant species unique to the rain forest have medicinal value; the author
needs only believe that there are some unknown rain forest plants with medicinal value that cannot
be found any other way.
Answer choice (D): While it would be comforting to believe that scientists will extract the full
medicinal value of all substances they encounter in the rain forest, this belief is not required for
the argument. Even if scientists are woefully inefficient at discover the full range of medicinally
valuable substances in the rain forest, preserving the rain forest may still be the only way to make
certain medical discoveries. The arguments requires that certain discoveries can only come from
substance in tropical rain forests, regardless of whether scientists are able to make all such potential
Answer choice (E): This is a value statement. The author’s argument that some discoveries would
be precluded by the failure to preserve to rain forest does not depend upon any particular value
judgment. Whether or not is it desirable to preserve rain forests and make important medical
discoveries, the conditional relationship between the two would be unchanged. Thus, even if the
author were not in favor of preserving rain forests, he could still believe that medical developments
depended on doing so.