Biologist: In Region X, the average horn mass and body length of adult

Explanation

Let's go through the passage and label the parts.

Part	Function
Biologist:	author
In Region X, the average horn mass and body length of adult bighorn sheep has dropped over the past several decades.	statement of fact
The cause is probably regulations prohibiting hunting of smaller animals.	main conclusion
These regulations have undoubtedly given smaller sheep an advantage in surviving to a reproductive age.	supporting information
Therefore, genes for smaller adult size most likely have spread through the population.	intermediate conclusion

It's a little tricky to decide whether "The cause is probably regulations prohibiting hunting of smaller animals," or "Therefore, genes for smaller adult size most likely have spread through the population," is the main conclusion.

At the same time, by noticing that "These regulations have undoubtedly given smaller sheep an advantage in surviving to a reproductive age. Therefore, genes for smaller adult size most likely have spread through the population," supports "The cause is probably regulations prohibiting hunting of smaller animals," we can decide that "The cause is probably regulations prohibiting hunting of smaller animals," is the main conclusion since it is supported by other statements in the passage but does not support anything else.

A The first is the main conclusion; the second is an observation for which a causal explanation is presented.

We could argue that the second part of this choice is correct since, in a way, "genes for smaller adult size most likely have spread through the population," is explained by "These regulations have undoubtedly given smaller sheep an advantage in surviving to a reproductive age."

However, this choice has a clear failure point in that the first statement is not a conclusion. It's just a fact about a phenomenon.

Eliminate.

B The first is a premise supporting the second; the second is the main conclusion, but not the only conclusion.

This choice is tricky because the second boldfaced portion could seem to be the main conclusion because it appears at the end of the passage and is preceded by "therefore." So, we could decide that the second boldfaced portion is the main conclusion and that the first boldfaced portion provides support since it's at the beginning of the passage.

However, as we discussed above, the second boldfaced portion is an intermediate conclusion rather than the main conclusion.

Also, the first boldfaced portion merely describes the situation and does not support the second.

Eliminate.

C The first describes a phenomenon for which the main conclusion presents an explanation; the second is a subsidiary conclusion supporting the main conclusion.

The first does describe a phenomenon for which the main conclusion, "The cause is probably regulations prohibiting hunting of smaller animals," presents an explanation.

Also, as we discussed above, the second is an intermediate, or subsidiary, conclusion that supports the main conclusion.

Keep

D The first is a subsidiary conclusion that supports the main conclusion; the second is a premise that independently supports the main conclusion.

This choice is almost completely incorrect since the first is not a subsidiary conclusion and does not support any conclusion and the second is an intermediate conclusion and thus does not support the main conclusion "independently." Rather, it supports the main conclusion by following from "These regulations have undoubtedly given smaller sheep an advantage in surviving to a reproductive age."

However, notice that the question-writer did make this choice a little tricky because the first part of this choice correctly describes the second boldfaced portion and because the second part of this choice is somewhat correct in that the second boldfaced portion does support the main conclusion. So, the question-writer made it possible that, if we're not careful, we could be tempted to choose this choice.

Eliminate.

E The first suggests a causal explanation for a phenomenon described by the main conclusion; the second provides further evidence to support that explanation.

This choice is incorrect. At the same time, it's interesting to see how the question writer made this choice tricky.

The first boldfaced portion is the phenomenon rather than the explanation for the phenomenon, but if we're not careful, we could see "phenomenon" in this choice and think that it correctly describes the first boldfaced portion.

Also, the second boldfaced portion does help to support the explanation.

So, this choice is a good example of an incorrect boldfaced answer choice that can trip us up if we fail to keep thing straight.

Eliminate.

Correct Answer